Question

evaluate using suitable identity -13^3-8^3+21^3

Answer 1

-13^3-8^3+21^3=(-13-8+21)^3=(-21+21)^3=0^3=0

Answer 2

= ( -13 )³ - 8³ + 21³

Let , ( a = -13 , b = -8 and c = 21 ).

Now,

= a + b + c

= -13 - 8 + 21

= -21 + 21

= 0.

So, a + b + c = 0.

Using identity , [ If ( a + b + c = 0 ),then a³ + b³ + c³ = 3abc ]

= 3 ( -13 ) (-8 ) 21

= 6,552.