Question

What value should be added to the expression to create a perfect square? x^2-20x

Answer 1

AX^2 + Bx + C is the usual form of a quadratic equation.
When you expand (a+b)^2 .... The last value is half of the middle and then squared

Answer 2

SO for your question, you half 20 then square it which is 20/2 = 10 ... 10^2 = 100

Therefore its 100