Algebraic equation using two operations

Question

The product of two numbers is -72. Their sum is 1. Find the smaller number.

Answer 1

xy=-72

x+y=1

x=1-y

substitute into the product equation

x(1-x)=-72

x - x² = -72

x² - x -72 = 0

(x-9)(x+8)=0

x=9 and he smaller number is -8