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f(x)=1ucos2tdtf(x) = \int_{1}^{u} \cos^2 t \, dt, where u=ln(x2+x1)u=\ln(x^2 +x-1)

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Q. f(x)=1ucos2tdtf(x) = \int_{1}^{u} \cos^2 t \, dt, where u=ln(x2+x1)u=\ln(x^2 +x-1)
  1. Apply Power-Reduction Formula: To solve the integral of cos2(t)\cos^2(t), we can use a power-reduction formula from trigonometry, which states that cos2(t)\cos^2(t) can be expressed as (1+cos(2t))/2(1 + \cos(2t))/2. This will simplify the integration process.
  2. Rewrite Integral Using Formula: Now, we rewrite the integral using the power-reduction formula:\newlinef(x)=1ln(x2+x1)1+cos(2t)2dtf(x) = \int_{1}^{\ln(x^2 + x - 1)} \frac{1 + \cos(2t)}{2} \, dt.
  3. Split Integral into Two: Next, we split the integral into two separate integrals: f(x)=121ln(x2+x1)1dt+121ln(x2+x1)cos(2t)dtf(x) = \frac{1}{2}\int_{1}^{\ln(x^2 + x - 1)} 1 \, dt + \frac{1}{2}\int_{1}^{\ln(x^2 + x - 1)} \cos(2t) \, dt.
  4. Integrate Each Part Separately: We can now integrate each part separately. The integral of 11 with respect to tt is simply tt, and the integral of cos(2t)\cos(2t) with respect to tt is (1/2)sin(2t)(1/2)\sin(2t) because the derivative of sin(2t)\sin(2t) is 2cos(2t)2\cos(2t), so we need to multiply by 1/21/2 to compensate for the derivative of the inside function.\newlinef(x)=(1/2)[t]f(x) = (1/2)[t] from 11 to tt11 + tt22 from 11 to tt11.
  5. Evaluate Integrals at Limits: Now we evaluate the integrals at the upper and lower limits: f(x)=12[ln(x2+x1)1]+14[sin(2ln(x2+x1))sin(2)]f(x) = \frac{1}{2}[\ln(x^2 + x - 1) - 1] + \frac{1}{4}[\sin(2\ln(x^2 + x - 1)) - \sin(2)].
  6. Simplify the Expression: Finally, we simplify the expression to get the final answer: f(x)=12ln(x2+x1)12+14sin(2ln(x2+x1))14sin(2)f(x) = \frac{1}{2}\ln(x^2 + x - 1) - \frac{1}{2} + \frac{1}{4}\sin(2\ln(x^2 + x - 1)) - \frac{1}{4}\sin(2).

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