Question

if x+y=5 and x 2 +y 2 =111 then x 3 +y 3 =?

Answer 1

x+y=5----(1)
x2+y2=111----(2)
square(1)
x^2+y^2+2xy=25
111+2xy=25
2xy=25-111
2xy=-86
xy=-43---(3)
x^3+y^3=(x+y)[x^2+y^2-xy]
=5×[111-(-43)]
=5[111+43]
=5×154
=770