Solve for x
x=-10
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\left(x-10\right)\left(x+10\right)-100=x\left(x+20\right)
Variable x cannot be equal to any of the values 0,10 since division by zero is not defined. Multiply both sides of the equation by x\left(x-10\right), the least common multiple of x,10x-x^{2},x-10.
x^{2}-100-100=x\left(x+20\right)
Consider \left(x-10\right)\left(x+10\right). Multiplication can be transformed into difference of squares using the rule: \left(a-b\right)\left(a+b\right)=a^{2}-b^{2}. Square 10.
x^{2}-200=x\left(x+20\right)
Subtract 100 from -100 to get -200.
x^{2}-200=x^{2}+20x
Use the distributive property to multiply x by x+20.
x^{2}-200-x^{2}=20x
Subtract x^{2} from both sides.
-200=20x
Combine x^{2} and -x^{2} to get 0.
20x=-200
Swap sides so that all variable terms are on the left hand side.
x=\frac{-200}{20}
Divide both sides by 20.
x=-10
Divide -200 by 20 to get -10.
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