So I am doing my algebra home work and I get stuck on these three problems.

Question

x^2-19x+72 from there idk what to do because nothing multiplies up to 72 and adds up to -19.

Same for this one.
x^2-25x+48

And
x^2+9-90
(X+15) (x-6)

Answer 1

I am assuming you are factoring ?

for x^2 - 19x + 72 there are no factors with rational numbers
(I found the discriminant b^2 - 4ac to be 649, which is not a perfect square, thus no factors)

x^2 - 25x - 90
same thing, b^2-4ac = 985 , no factors

I assume a typo in the 3rd and you meant:
x^2 + 9x - 90

which does factor to (x+15)(x-6)