Question

What number should be added to both sides of the equation to complete the square? X^2-10=7

Answer 1

I must assume that you meant X^2-10x =7. If that is indeed the case, then:

X^2-10x =7 => x^2 -10x + 25 - 25 = 7, so that (x-5)^2 = 32 (Add 25, then
subtract 25)
Then x-5 = plus or minus sqrt(16)sqrt(2) = 4sqrt(2).

Then x = 5 plus or minus 4 sqrt(2) (answers)