Question

2 X + 3 Y is equal to 13 and xy =6 find the value of 8 x cube + 27 y cube

Answer 1

xy=6.......(1)
2x+3y=13...(2)
=8x3+27y3
=(2x)3 +(3y)3
=(2x+3y)3 _3× 2x × 3y(2x+3y) using (a+b)3
=(13)3_18×6×13(from 1 and 2)
=2197-1404
=793

Answer 2

Given x+y=13 and xy=6
Recall, x3 + y3 = (x + y)3 – 3xy(x + y)
=x3 + y3 =( 13)^3-8(27)(13)
=-2808-2197
=611