Question

21 xy -9 x + 7 y-3
$21xy - 9x + 7y - 3$
​

Answer 1

Using Rule 8,
Given, x + y = 7
Now, x3 + y3 + 21xy = (x + y)3 – 3xy(x + y) + 21xy
= (7)3 – 3xy(7) + 21xy
= 343 – 21xy + 21xy = 343

Answer 2

3x( 7y-3) + 1(7y-3)
(3x+1) (7y-3)