Question

without calculating the cubes find the value of (20)³ + (- 15)³ + (- 5)³​

Answer 1

Answer:

Step-by-step explanation:

a³+b³+c³ = (a + b + c) (a² + b² + c² – ab – bc – ca) + 3abc.

a = 28, b = -15 and c = -13

→ = (28)³+(-15)³+(-13)³

→ = (28+(-15)+(-13)) ((28)²+(-15)²+(-13)²-(28)(-15)-(-15)(-13)-(-13)(28)) + 3(28)(-15)(-13)

→ = (28-15-13) ((28)²+(-15)²+(-13)²-(28)(-15)-(-15)(-13)-(-13)(28)) + 3(28)(195)

→ = (28-28)((28)²+(-15)²+(-13)²-(28)(-15)-(-15)(-13)-(-13)(28))+(84)(195)

→ = 0 ((28)²+(-15)²+(-13)²-(28)(-15)-(-15)(-13)-(-13)(28)) + 16380

→ = 0 + 16380

→ = 16380

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