Question

4x+5z=19 and xz=5. find 64x³+125z³

Answer 1

as (4x+5z) = 19

then cube on both sides,

(4x+5z)^3 = 19^3

by formula (a+b)^3 = a^3 + b^3 +3ab(a+b)

here,

64x^3 +125z^3 +3(4x*5z){4x+5z}  = 6859

64x^3 +125x^3 +60{5} {19} = 6859

64x^3+125x^3 +5700 = 6859

64x^3 +125z^3 =6859-5700

64x^3 +125z^3 = 1159




i hope this will help you 



- by ABHAY