How do you simplify (x+3)(x-5)

so i thought you would use the F.O.I.L. method (multiply x by a and -5 and then multiply 3 by x and -5)
but on the paper (someone else's im borrowing for practice) he circled the answer: x squared - 15

idk which is roght. plz help. ty

Yes you would foil. x^2 -15 is wrong because it leaves out the middle terms which can be revealed by foiling.
F.O.I.L = First, Outer, Inner, Last
(x+3)(x-5) = x*x + x*(-5) + 3*x + 3*(-5)
= x^2 - 5x + 3x - 15
= x^2 - 2x - 15

yes you do use the foil method. By using the foil method your answer should x^2 -2x-15. (x squared minus 2x minus 15. The person you borrowed the paper for practice has the wrong answer that person just multiplied x with x and 3 with 5.

(I assume this is set equal to zero)

It is already simplified. To solve, set each quantity equal to zero:
x+3=0
x=-3
and
x-5=0
x=5

The solution are: x= -3, and x=5



If you wanted to UNsimplify it:
(x+3)(x-5)
(x^2)-5x+3x-15=0
(x^2)-2x-15=0

Whoever's paper you were using is incorrect. You were correct to use FOIL:
x*x+x*(-5)+3*x+3*(-5)
x^2-2x-15

The person is incorrect.

The correct answer is: x² - 2x - 15

x^2 - 2x - 15

X^2 -2x -15