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If ddx(f(x))=4x3−3x4\frac{d}{dx}(f(x)) = 4x^{3} - \frac{3}{x^{4}} dxd​(f(x))=4x3−x43​​ and f(2)=0, f(2) = 0,f(2)=0,  then  f(
Question

If ddx(f(x))=4x33x4\frac{d}{dx}(f(x)) = 4x^{3} - \frac{3}{x^{4}} ​ and f(2)=0, f(2) = 0,  then  f(x)f(x)  is:

A.

x4+1x3+1298x^{4} + \frac{1}{x^{3}} + \frac{129}{8} ​​

B.

x4+1x31298x^{4} + \frac{1}{x^{3}} - \frac{129}{8} ​​

C.

x3+1x4+1298x^{3} + \frac{1}{x^{4}} + \frac{129}{8} ​​

D.

x3+1x41298 x^{3} + \frac{1}{x^{4}} - \frac{129}{8}​​

Correct option is B

Given:
dfdx=4x33x4\frac{df}{dx} = 4x^{3} - \frac{3}{x^{4}}​​
Concept used:
Integrate both sides to find f(x). f(x).​​
Solution:
f(x)=(4x33x4)dx=4x3dx3x4dx=x4+x3+C=x4+1x3+Cf(x) = \int \left(4x^{3} - \frac{3}{x^{4}}\right) dx \\= \int 4x^{3} dx - \int 3x^{-4} dx \\= x^{4} + x^{-3} + C \\= x^{4} + \frac{1}{x^{3}} + C​​
Given f(2)=0: f(2) = 0:​​
0=24+123+C 0=16+18+C C=12980 = 2^{4} + \frac{1}{2^{3}} + C \\ \ \\0 = 16 + \frac{1}{8} + C \\ \ \\C = -\frac{129}{8}​​
Thus, f(x)=x4+1x31298f(x) = x^{4} + \frac{1}{x^{3}} - \frac{129}{8}​​
Correct answer is (b)  x4+1x31298\ x^{4} + \frac{1}{x^{3}} - \frac{129}{8}​​

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