How do I write a quadratic function whose zeroes are -3 and -5?

Answer 1

In general if the zeroes are a and b, the factorisation will be c (x-a) (x-b), where c is a constant.

So you can choose c = 1

and a = -3 and b = -5 so as Neha said factorisation will be (x+3) (x+5)

You can multiply out by foiling

x +5

x x² +5x

+3 +3x 15

giving x² + 8x + 15

[ you can plot this on Desmos and check it crosses the x axis at x=-3 and -5 if you wish]

Answer 2

(x+3)(x+5)

x²+8x+15