. the valu of x
Let x be real number such that x3 + 4x = 8, then the value of x7 + 64x2 is ...
A. 136
B. 146
C. 128
D. 156
Best Answer
Answer ||| C
Solution |||
x3 + 4x = 8
…(1)
x7 + 64x2 =
⇒ (x3)2.x + 64x2
⇒ (8 – 4x)2x + 64x2
⇒ (64 + 16x2 – 64x)x + 64x2
⇒ 64x + 16x3 – 64x2 + 64x2
16(x3 + 4x) = 16(8) = 128
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