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84=0,7*4200*0,3/21*log(2)60-20/x-20

84=0,7*4200*0,3/21*log(2)60-20/x-20 equation

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Numerical solution:

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The solution

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                    1              20     
84 = 7/10*4200*3/10*--*log(2)*60 - -- - 20
                    21             x      
$$84 = \left(-1\right) 20 + \frac{7}{10} \cdot 4200 \cdot \frac{3}{10} \cdot \frac{1}{21} \log{\left(2 \right)} 60 - \frac{20}{x}$$
Detail solution
Given the equation:
$$84 = \left(-1\right) 20 + \frac{7}{10} \cdot 4200 \cdot \frac{3}{10} \cdot \frac{1}{21} \log{\left(2 \right)} 60 - \frac{20}{x}$$
Use proportions rule:
From $\frac{a_1}{b1} = \frac{a_2}{b_2}$ should $a_1*b_2 = a_2*b_1$,
In this case
a1 = 1

b1 = 1/(104 - 2520*log(2))

a2 = 1

b2 = -x/20

so we get the equation
$$1 \left(- \frac{x}{20}\right) = 1 \cdot \frac{1}{- 2520 \log{\left(2 \right)} + 104}$$
$$- \frac{x}{20} = \frac{1}{- 2520 \log{\left(2 \right)} + 104}$$
Expand brackets in the right part
-x/20 = 1/104+1/2520*log+1/2)

Divide both parts of the equation by -1/20
x = 1/(104 - 2520*log(2)) / (-1/20)

We get the answer: x = 5/(2*(-13 + 315*log(2)))
The graph
Rapid solution [src]
               5          
x_1 = --------------------
      2*(-13 + 315*log(2))
$$x_{1} = \frac{5}{2 \left(-13 + 315 \log{\left(2 \right)}\right)}$$
Sum and product of roots [src]
sum
         5          
--------------------
2*(-13 + 315*log(2))
$$\left(\frac{5}{2 \left(-13 + 315 \log{\left(2 \right)}\right)}\right)$$
=
         5          
--------------------
2*(-13 + 315*log(2))
$$\frac{5}{2 \left(-13 + 315 \log{\left(2 \right)}\right)}$$
product
         5          
--------------------
2*(-13 + 315*log(2))
$$\left(\frac{5}{2 \left(-13 + 315 \log{\left(2 \right)}\right)}\right)$$
=
         5          
--------------------
2*(-13 + 315*log(2))
$$\frac{5}{2 \left(-13 + 315 \log{\left(2 \right)}\right)}$$
Numerical answer [src]
x1 = 0.0121748486381668
x1 = 0.0121748486381668
The graph
84=0,7*4200*0,3/21*log(2)60-20/x-20 equation