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(3)/(8y^3+1)-(1)/(2y+1)=(y+3)/(y^2-2y+1) equation

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Numerical solution:

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The solution

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   3          1         y + 3    
-------- - ------- = ------------
   3       2*y + 1    2          
8*y  + 1             y  - 2*y + 1
$$\frac{3}{8 y^{3} + 1} - \frac{1}{2 y + 1} = \frac{y + 3}{\left(y^{2} - 2 y\right) + 1}$$
The graph
Sum and product of roots [src]
sum
                                     ______________     /           ______________                          \                                        ______________     /             ______________                          \              ______________                         
                                    /         ____      |          /         ____                           |                                       /         ____      |            /         ____                           |             /         ____                          
                                   /  221   \/ 67       |  ___    /  221   \/ 67                            |                                      /  221   \/ 67       |    ___    /  221   \/ 67                            |            /  221   \/ 67                           
                                3 /   --- + ------      |\/ 3 *3 /   --- + ------               ___         |                                   3 /   --- + ------      |  \/ 3 *3 /   --- + ------               ___         |         3 /   --- + ------                          
  2              1              \/    108     4         |      \/    108     4                \/ 3          |     2              1              \/    108     4         |        \/    108     4                \/ 3          |     2   \/    108     4                 1           
- - - ----------------------- + ------------------- + I*|------------------------- + -----------------------| + - - - ----------------------- + ------------------- + I*|- ------------------------- - -----------------------| + - - - ------------------- + ----------------------
  9            ______________            6              |            6                        ______________|     9            ______________            6              |              6                        ______________|     9            3                    ______________
              /         ____                            |                                    /         ____ |                 /         ____                            |                                      /         ____ |                                      /         ____ 
             /  221   \/ 67                             |                                   /  221   \/ 67  |                /  221   \/ 67                             |                                     /  221   \/ 67  |                                     /  221   \/ 67  
      108*3 /   --- + ------                            |                            108*3 /   --- + ------ |         108*3 /   --- + ------                            |                              108*3 /   --- + ------ |                               54*3 /   --- + ------ 
          \/    108     4                               \                                \/    108     4    /             \/    108     4                               \                                  \/    108     4    /                                  \/    108     4    
$$\left(- \frac{\sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}}{3} - \frac{2}{9} + \frac{1}{54 \sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}}\right) + \left(\left(- \frac{2}{9} - \frac{1}{108 \sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}} + \frac{\sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}}{6} + i \left(- \frac{\sqrt{3} \sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}}{6} - \frac{\sqrt{3}}{108 \sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}}\right)\right) + \left(- \frac{2}{9} - \frac{1}{108 \sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}} + \frac{\sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}}{6} + i \left(\frac{\sqrt{3}}{108 \sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}} + \frac{\sqrt{3} \sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}}{6}\right)\right)\right)$$
=
        /             ______________                          \     /           ______________                          \
        |            /         ____                           |     |          /         ____                           |
        |    ___    /  221   \/ 67                            |     |  ___    /  221   \/ 67                            |
        |  \/ 3 *3 /   --- + ------               ___         |     |\/ 3 *3 /   --- + ------               ___         |
  2     |        \/    108     4                \/ 3          |     |      \/    108     4                \/ 3          |
- - + I*|- ------------------------- - -----------------------| + I*|------------------------- + -----------------------|
  3     |              6                        ______________|     |            6                        ______________|
        |                                      /         ____ |     |                                    /         ____ |
        |                                     /  221   \/ 67  |     |                                   /  221   \/ 67  |
        |                              108*3 /   --- + ------ |     |                            108*3 /   --- + ------ |
        \                                  \/    108     4    /     \                                \/    108     4    /
$$- \frac{2}{3} + i \left(- \frac{\sqrt{3} \sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}}{6} - \frac{\sqrt{3}}{108 \sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}}\right) + i \left(\frac{\sqrt{3}}{108 \sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}} + \frac{\sqrt{3} \sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}}{6}\right)$$
product
/                                     ______________     /           ______________                          \\ /                                     ______________     /             ______________                          \\ /           ______________                         \
|                                    /         ____      |          /         ____                           || |                                    /         ____      |            /         ____                           || |          /         ____                          |
|                                   /  221   \/ 67       |  ___    /  221   \/ 67                            || |                                   /  221   \/ 67       |    ___    /  221   \/ 67                            || |         /  221   \/ 67                           |
|                                3 /   --- + ------      |\/ 3 *3 /   --- + ------               ___         || |                                3 /   --- + ------      |  \/ 3 *3 /   --- + ------               ___         || |      3 /   --- + ------                          |
|  2              1              \/    108     4         |      \/    108     4                \/ 3          || |  2              1              \/    108     4         |        \/    108     4                \/ 3          || |  2   \/    108     4                 1           |
|- - - ----------------------- + ------------------- + I*|------------------------- + -----------------------||*|- - - ----------------------- + ------------------- + I*|- ------------------------- - -----------------------||*|- - - ------------------- + ----------------------|
|  9            ______________            6              |            6                        ______________|| |  9            ______________            6              |              6                        ______________|| |  9            3                    ______________|
|              /         ____                            |                                    /         ____ || |              /         ____                            |                                      /         ____ || |                                   /         ____ |
|             /  221   \/ 67                             |                                   /  221   \/ 67  || |             /  221   \/ 67                             |                                     /  221   \/ 67  || |                                  /  221   \/ 67  |
|      108*3 /   --- + ------                            |                            108*3 /   --- + ------ || |      108*3 /   --- + ------                            |                              108*3 /   --- + ------ || |                            54*3 /   --- + ------ |
\          \/    108     4                               \                                \/    108     4    // \          \/    108     4                               \                                  \/    108     4    // \                               \/    108     4    /
$$\left(- \frac{2}{9} - \frac{1}{108 \sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}} + \frac{\sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}}{6} + i \left(\frac{\sqrt{3}}{108 \sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}} + \frac{\sqrt{3} \sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}}{6}\right)\right) \left(- \frac{2}{9} - \frac{1}{108 \sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}} + \frac{\sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}}{6} + i \left(- \frac{\sqrt{3} \sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}}{6} - \frac{\sqrt{3}}{108 \sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}}\right)\right) \left(- \frac{\sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}}{3} - \frac{2}{9} + \frac{1}{54 \sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}}\right)$$
=
-1/6
$$- \frac{1}{6}$$
-1/6
Rapid solution [src]
                                          ______________     /           ______________                          \
                                         /         ____      |          /         ____                           |
                                        /  221   \/ 67       |  ___    /  221   \/ 67                            |
                                     3 /   --- + ------      |\/ 3 *3 /   --- + ------               ___         |
       2              1              \/    108     4         |      \/    108     4                \/ 3          |
y1 = - - - ----------------------- + ------------------- + I*|------------------------- + -----------------------|
       9            ______________            6              |            6                        ______________|
                   /         ____                            |                                    /         ____ |
                  /  221   \/ 67                             |                                   /  221   \/ 67  |
           108*3 /   --- + ------                            |                            108*3 /   --- + ------ |
               \/    108     4                               \                                \/    108     4    /
$$y_{1} = - \frac{2}{9} - \frac{1}{108 \sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}} + \frac{\sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}}{6} + i \left(\frac{\sqrt{3}}{108 \sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}} + \frac{\sqrt{3} \sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}}{6}\right)$$
                                          ______________     /             ______________                          \
                                         /         ____      |            /         ____                           |
                                        /  221   \/ 67       |    ___    /  221   \/ 67                            |
                                     3 /   --- + ------      |  \/ 3 *3 /   --- + ------               ___         |
       2              1              \/    108     4         |        \/    108     4                \/ 3          |
y2 = - - - ----------------------- + ------------------- + I*|- ------------------------- - -----------------------|
       9            ______________            6              |              6                        ______________|
                   /         ____                            |                                      /         ____ |
                  /  221   \/ 67                             |                                     /  221   \/ 67  |
           108*3 /   --- + ------                            |                              108*3 /   --- + ------ |
               \/    108     4                               \                                  \/    108     4    /
$$y_{2} = - \frac{2}{9} - \frac{1}{108 \sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}} + \frac{\sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}}{6} + i \left(- \frac{\sqrt{3} \sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}}{6} - \frac{\sqrt{3}}{108 \sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}}\right)$$
                ______________                         
               /         ____                          
              /  221   \/ 67                           
           3 /   --- + ------                          
       2   \/    108     4                 1           
y3 = - - - ------------------- + ----------------------
       9            3                    ______________
                                        /         ____ 
                                       /  221   \/ 67  
                                 54*3 /   --- + ------ 
                                    \/    108     4    
$$y_{3} = - \frac{\sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}}{3} - \frac{2}{9} + \frac{1}{54 \sqrt[3]{\frac{221}{108} + \frac{\sqrt{67}}{4}}}$$
y3 = -(221/108 + sqrt(67)/4)^(1/3)/3 - 2/9 + 1/(54*(221/108 + sqrt(67)/4)^(1/3))
Numerical answer [src]
y1 = 0.0385827652803931 + 0.471779867138517*i
y2 = 0.0385827652803931 - 0.471779867138517*i
y3 = -0.743832197227453
y3 = -0.743832197227453