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(x-9)(x-a)=x^2-4ax+b equation

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Numerical solution:

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The solution

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(x - 9)*(x - a) = x  - 4*a*x + b
$$\left(- a + x\right) \left(x - 9\right) = b + \left(- 4 a x + x^{2}\right)$$
Detail solution
Given the linear equation:
(x-9)*(x-a) = x^2-4*a*x+b

Expand brackets in the left part
x-9x-a = x^2-4*a*x+b

Looking for similar summands in the left part:
(-9 + x)*(x - a) = x^2-4*a*x+b

Move free summands (without b)
from left part to right part, we given:
$$\left(- a + x\right) \left(x - 9\right) + 9 = - 4 a x + b + x^{2} + 9$$
Move the summands with the unknown b
from the right part to the left part:
$$- b + \left(- a + x\right) \left(x - 9\right) + 9 = - 4 a x + x^{2} + 9$$
Divide both parts of the equation by (9 - b + (-9 + x)*(x - a))/b
b = 9 + x^2 - 4*a*x / ((9 - b + (-9 + x)*(x - a))/b)

We get the answer: b = -9*x + 9*a + 3*a*x
The graph
Sum and product of roots [src]
sum
-9*re(x) + 3*re(a*x) + 9*re(a) + I*(-9*im(x) + 3*im(a*x) + 9*im(a))
$$i \left(9 \operatorname{im}{\left(a\right)} - 9 \operatorname{im}{\left(x\right)} + 3 \operatorname{im}{\left(a x\right)}\right) + 9 \operatorname{re}{\left(a\right)} - 9 \operatorname{re}{\left(x\right)} + 3 \operatorname{re}{\left(a x\right)}$$
=
-9*re(x) + 3*re(a*x) + 9*re(a) + I*(-9*im(x) + 3*im(a*x) + 9*im(a))
$$i \left(9 \operatorname{im}{\left(a\right)} - 9 \operatorname{im}{\left(x\right)} + 3 \operatorname{im}{\left(a x\right)}\right) + 9 \operatorname{re}{\left(a\right)} - 9 \operatorname{re}{\left(x\right)} + 3 \operatorname{re}{\left(a x\right)}$$
product
-9*re(x) + 3*re(a*x) + 9*re(a) + I*(-9*im(x) + 3*im(a*x) + 9*im(a))
$$i \left(9 \operatorname{im}{\left(a\right)} - 9 \operatorname{im}{\left(x\right)} + 3 \operatorname{im}{\left(a x\right)}\right) + 9 \operatorname{re}{\left(a\right)} - 9 \operatorname{re}{\left(x\right)} + 3 \operatorname{re}{\left(a x\right)}$$
=
-9*re(x) + 3*re(a*x) + 9*re(a) + 3*I*(-3*im(x) + 3*im(a) + im(a*x))
$$3 i \left(3 \operatorname{im}{\left(a\right)} - 3 \operatorname{im}{\left(x\right)} + \operatorname{im}{\left(a x\right)}\right) + 9 \operatorname{re}{\left(a\right)} - 9 \operatorname{re}{\left(x\right)} + 3 \operatorname{re}{\left(a x\right)}$$
-9*re(x) + 3*re(a*x) + 9*re(a) + 3*i*(-3*im(x) + 3*im(a) + im(a*x))
Rapid solution [src]
b1 = -9*re(x) + 3*re(a*x) + 9*re(a) + I*(-9*im(x) + 3*im(a*x) + 9*im(a))
$$b_{1} = i \left(9 \operatorname{im}{\left(a\right)} - 9 \operatorname{im}{\left(x\right)} + 3 \operatorname{im}{\left(a x\right)}\right) + 9 \operatorname{re}{\left(a\right)} - 9 \operatorname{re}{\left(x\right)} + 3 \operatorname{re}{\left(a x\right)}$$
b1 = i*(9*im(a) - 9*im(x) + 3*im(a*x)) + 9*re(a) - 9*re(x) + 3*re(a*x)