14. Without actually calculating the cubes, find the value of each of the following:
(i) (-12)3 + (7)3 + (5)3
(ü) (28) +(-15)3 +(-13)3
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Answer:
(-12)³ + (7)³+ (5)³
Let x = -12, y =7&z=5
x + y + z = -12 + 7 + 5 = 0
Here, x + y + z = 0
We know that if,
x + y + z = 0, then x³ + y³ + z³ = 3xyz (-12)³ + (7)³ + (5)³ = 3(-12)(7)(5) = -1260
(-12) ³+ (7)³+ (5)³ = - 1260
(ii) (28)3 + (-15)³ + (-13)³
Let x = 28, y = -15 and z = -13
x + y + z = 28-15-13 = 0
Here, x + y + z = 0
We know that if, x + y + z = 0,
then x³ + y² + z³ = 3xyz
(28)3³+ (-15)3 + (-13)³ = 3(28)(-15)(-13)
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