Question

2a + 2b + 2c = 10 and ab + bc + ca = 40 find a cube + b cube + c cube - 3ab

Answer 1

a cube + b cube + c cube - 3ab= (a+b+c)2
$5 \times 5 = 25$
2a+2b+2c=10
2(a+b+c)=2 ×5
2 and 2 get cancelled
a+b+c=5
(a+b+c)2= 5×5
=25