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0πsin(3x+π2)dx\int_{0}^{\pi}\sin(3x+\frac{\pi}{2})dx

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Q. 0πsin(3x+π2)dx\int_{0}^{\pi}\sin(3x+\frac{\pi}{2})dx
  1. Apply Trigonometric Identity: We need to evaluate the integral of sin(3x+(π/2))\sin(3x + (\pi/2)) from 00 to π\pi. To simplify the integral, we can use the trigonometric identity sin(a+b)=sin(a)cos(b)+cos(a)sin(b)\sin(a + b) = \sin(a)\cos(b) + \cos(a)\sin(b). In this case, a=3xa = 3x and b=(π/2)b = (\pi/2), so sin(b)=1\sin(b) = 1 and cos(b)=0\cos(b) = 0. This simplifies the integral to just the integral of sin(3x)\sin(3x).
  2. Use Substitution Method: Now we can write the integral as: \newline0πsin(3x)dx\int_{0}^{\pi}\sin(3x)\,dx\newlineTo integrate sin(3x)\sin(3x), we use the substitution u=3xu = 3x, which implies du=3dxdu = 3dx or dx=du3dx = \frac{du}{3}.
  3. Change Limits of Integration: Substituting uu and dxdx into the integral, we get:\newline03πsin(u)(du3)\int_{0}^{3\pi}\sin(u)\left(\frac{du}{3}\right)\newlineThe limits of integration have also changed because when x=0x = 0, u=0u = 0, and when x=πx = \pi, u=3πu = 3\pi.
  4. Evaluate Integral of sin(u)\sin(u): The integral now becomes: (13)03πsin(u)du(\frac{1}{3})\int_{0}^{3\pi}\sin(u)\,du The integral of sin(u)\sin(u) with respect to uu is cos(u)-\cos(u), so we have: (13)(cos(u))(\frac{1}{3})(-\cos(u)) evaluated from 00 to 3π3\pi.
  5. Final Simplification: Evaluating the antiderivative at the bounds, we get:\newline(13)(cos(3π))(13)(cos(0))(\frac{1}{3})(-\cos(3\pi)) - (\frac{1}{3})(-\cos(0))\newlineWe know that cos(3π)=1\cos(3\pi) = -1 and cos(0)=1\cos(0) = 1, so the expression simplifies to:\newline(13)(1)(13)(1)=(13)+(13)=23(\frac{1}{3})(1) - (\frac{1}{3})(-1) = (\frac{1}{3}) + (\frac{1}{3}) = \frac{2}{3}.

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