Write this in y=ax^2+b form:
y=(x-5)^2 - 2

Expand (x - 5)^2

(x - 5)^2 = (x - 5)(x - 5)

Multiply all the terms in the first parenthesis to all the terms in the 2nd:

x * x = x^2
x * -5 = -5x
-5 * x = -5x
-5 * -5 = 25

So we have:

x^2 - 5x - 5x + 25

Combine like terms:

x^2 - 10x + 25

Plug it back in:

y = (x - 5)^2 - 2

y = x^2 - 10x + 25 - 2

Combine like terms:

y = x^2 - 10x + 23