(10+x)(10-x)=91

Solution for (10+x)(10-x)=91 equation:

Simplifying
(10 + x)(10 + -1x) = 91

Multiply (10 + x) * (10 + -1x)
(10(10 + -1x) + x(10 + -1x)) = 91
((10 * 10 + -1x * 10) + x(10 + -1x)) = 91
((100 + -10x) + x(10 + -1x)) = 91
(100 + -10x + (10 * x + -1x * x)) = 91
(100 + -10x + (10x + -1x2)) = 91

Combine like terms: -10x + 10x = 0
(100 + 0 + -1x2) = 91
(100 + -1x2) = 91

Solving
100 + -1x2 = 91

Solving for variable 'x'.

Move all terms containing x to the left, all other terms to the right.

Add '-100' to each side of the equation.
100 + -100 + -1x2 = 91 + -100

Combine like terms: 100 + -100 = 0
0 + -1x2 = 91 + -100
-1x2 = 91 + -100

Combine like terms: 91 + -100 = -9
-1x2 = -9

Divide each side by '-1'.
x2 = 9

Simplifying
x2 = 9

Take the square root of each side:
x = {-3, 3}