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Evaluate the integral.

int-x cos(-2x+6)dx
Answer:

Evaluate the integral.\newlinexcos(2x+6)dx \int-x \cos (-2 x+6) d x \newlineAnswer:

Full solution

Q. Evaluate the integral.\newlinexcos(2x+6)dx \int-x \cos (-2 x+6) d x \newlineAnswer:
  1. Write Integral: Write down the integral to be solved.\newlineI=xcos(2x+6)dxI = \int -x \cos(-2x+6)\,dx
  2. Use Substitution: Use substitution to simplify the integral. Let u=2x+6u = -2x + 6, then du=2dxdu = -2dx. We need to express dxdx in terms of dudu, so dx=du2dx = -\frac{du}{2}. Also, when u=2x+6u = -2x + 6, x=6u2x = \frac{6 - u}{2}.I=(6u2)cos(u)(du2)I = \int -\left(\frac{6 - u}{2}\right) \cos(u) \left(-\frac{du}{2}\right)
  3. Simplify Integral: Simplify the integral by distributing the constants.\newlineI=(14)(6u)cos(u)duI = \int(\frac{1}{4})(6 - u) \cos(u) \, du\newlineI=(14)6cos(u)du(14)ucos(u)duI = (\frac{1}{4})\int 6\cos(u) \, du - (\frac{1}{4})\int u\cos(u) \, du
  4. Split and Solve: Split the integral into two parts and solve each part separately.\newlineFirst part: (14)6cos(u)du(\frac{1}{4})\int 6\cos(u) \, du\newlineSecond part: 14ucos(u)du-\frac{1}{4}\int u\cos(u) \, du
  5. Integrate First Part: Integrate the first part using the basic integral of cos(u)\cos(u).\newlineFirst part: (1/4)6cos(u)du=(1/4)(6sin(u))+C1(1/4)\int 6\cos(u) \, du = (1/4)(6\sin(u)) + C_1
  6. Integrate Second Part: Integrate the second part using integration by parts. Let v=uv = u and dw=cos(u)dudw = \cos(u) du. Then dv=dudv = du and w=sin(u)w = \sin(u).
    Second part: -\frac{\(1\)}{\(4\)}\int u\cos(u) du = -\frac{\(1\)}{\(4\)}(u\sin(u) - \int \sin(u) du) = -\frac{\(1\)}{\(4\)}(u\sin(u) + \cos(u)) + C_2
  7. Combine Results: Combine the results from step \(5 and step 66.\newlineI=(14)(6sin(u))(14)(usin(u)+cos(u))+CI = \left(\frac{1}{4}\right)(6\sin(u)) - \left(\frac{1}{4}\right)(u\sin(u) + \cos(u)) + C
  8. Substitute Back: Substitute back u=2x+6u = -2x + 6 into the integral.I=14(6sin(2x+6))14((2x+6)sin(2x+6)+cos(2x+6))+CI = \frac{1}{4}(6\sin(-2x + 6)) - \frac{1}{4}((-2x + 6)\sin(-2x + 6) + \cos(-2x + 6)) + C
  9. Final Simplification: Simplify the expression. \newlineI=32sin(2x+6)+12xsin(2x+6)14cos(2x+6)+CI = \frac{3}{2}\sin(-2x + 6) + \frac{1}{2}x\sin(-2x + 6) - \frac{1}{4}\cos(-2x + 6) + C