Question

If 3x + 4y = 5 and xy = 3, find 27x3- 64y3

Answer 1

(3x-4y)²= (3x+4y)²-4xy= 5²-4×3= 25-12= 13
3x-4y= √13

27x³-64y³= (3x-4y)³+3×3x×4y(3x-4y)= (√13)³+36×3(√13)= 13√13+108√13= 121√13