Question

What number must you add to complete the square
x^2-20x=17

Answer 1

100

Explanation:

10^2=100

Answer 2

`(*)\ (a-b)^2=a^2-2ab+b^2`

`x^2-20x=17\\\\x^2-2\cdot x\cdot10=17\ \ \ |+10^2\\\\\underbrace{x^2-2\cdot x\cdot10+10^2}_((*))=17+10^2\\\\(x-10)^2=117`

Answer: 10² = 100