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MHT CET · Maths · Indefinite Integration

If \(f^{\prime}(x)=k(\cos x-\sin x), f^{\prime}(0)=3, f\left(\frac{\pi}{2}\right)=15\), then \(f(x)=\)

  1. A \(3(\sin x+\cos x)+12\)
  2. B \(3(\sin x+\cos x)-12\)
  3. C \(-3(\sin x+\cos x)-12\)
  4. D \(12(\sin x+\cos x)+3\)
Verified Solution

Answer & Solution

Correct Answer

(A) \(3(\sin x+\cos x)+12\)

Step-by-step Solution

Detailed explanation

\(f^{\prime}(x)=k(\cos x-\sin x)\)
\(f^{\prime}(0)=3 \quad f(\pi / 2)=15\)
\(k=3\) then \(f(x)=8\)
Integrate \(f^{\prime}(x)\)
\(f(x)=k \sin x+k \cos x+c\)
\(f(x)=3 \sin x+3 \cos x+c\)
\(f(\pi / 2)=15\)
\(c+3=15\)
\(c=12\)
\(f(x)=3 \sin x+3 \cos x+12\)