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Grade: 11 

                        
if x^3 + 4x =8 find value of x^7 +64x^2 a)132 b)128 c)216 d)125
8 years ago

Answers : (1)

Sher Mohammad
IIT Delhi
askIITians Faculty
174 Points 
							x^3 +4x=8 square the equation
x^6 +16x^2 +8x^4=64 multiply with x
x^7+16x^3+8x^5-64x=0

now x^7+64x^2 put value of x^7
64x-16x^3-8x^5+64x^2
64x-8x^2(x^3+4x)+16x^3+64x^2
64x-64x^2+16x^3+64x^2
64x+16x^3
16(x^3+4x)=16*8=128
ans is B

Sher Mohammad
faculty askiitians
6 years ago
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