Question

the sum of two numbers is 9 and their product is 20 find the sum of their cubes and squares

Answer 1

xy=20 eq1

x+y=9
x=9-y

substitute value of x in eq1
xy=20
(9-y)y=20
9y-y^2=20
20-9y+y^2=0
y^2-9y+20=0
y^2-5y-4y+20=0
y(y-5)-4 (y-5)=0
(y-5)(y-4)
y=5 or y=4