求

  1. (a)

    ∫tan⁡2(x−1) dx,\int \tan^2(x - 1) \text{ d}x ,

  2. (b)

    ∫sin⁡−12x dx.\int \sin^{-1} 2x \text{ d}x .

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完整解法

3(a)

1. Rewrite the integrand using the trigonometric identity $\tan^2 \theta = \sec^2 \theta - 1$.

∫tan⁡2(x−1) dx=∫(sec⁡2(x−1)−1) dx\int \tan^2(x - 1) \text{ d}x = \int (\sec^2(x - 1) - 1) \text{ d}x

2. Integrate term-by-term and add the constant of integration.

=tan⁡(x−1)−x+C= \tan(x - 1) - x + C

答案

tan⁡(x−1)−x+C\tan(x - 1) - x + C

3(b)

1. Set up integration by parts by identifying $u$ and $\frac{dv}{dx}$.

∫sin⁡−12x dx=∫1⋅sin⁡−12x dx\int \sin^{-1} 2x \text{ d}x = \int 1 \cdot \sin^{-1} 2x \text{ d}x
Let u=sin⁡−12x  ⟹  dudx=21−(2x)2=21−4x2u = \sin^{-1} 2x \implies \frac{du}{dx} = \frac{2}{\sqrt{1 - (2x)^2}} = \frac{2}{\sqrt{1 - 4x^2}}
Let dvdx=1  ⟹  v=x\frac{dv}{dx} = 1 \implies v = x

2. Apply the integration by parts formula $\int u \text{ d}v = uv - \int v \text{ d}u$.

∫sin⁡−12x dx=xsin⁡−12x−∫x(21−4x2) dx\int \sin^{-1} 2x \text{ d}x = x \sin^{-1} 2x - \int x \left( \frac{2}{\sqrt{1 - 4x^2}} \right) \text{ d}x
=xsin⁡−12x−∫2x1−4x2 dx= x \sin^{-1} 2x - \int \frac{2x}{\sqrt{1 - 4x^2}} \text{ d}x

3. Evaluate the remaining integral using reverse chain rule (substitution) and add the constant of integration.

Consider ∫2x1−4x2 dx\int \frac{2x}{\sqrt{1 - 4x^2}} \text{ d}x:
=−14∫−8x(1−4x2)−12 dx= -\frac{1}{4} \int -8x (1 - 4x^2)^{-\frac{1}{2}} \text{ d}x
=−14((1−4x2)1212)=−121−4x2= -\frac{1}{4} \left( \frac{(1 - 4x^2)^{\frac{1}{2}}}{\frac{1}{2}} \right) = -\frac{1}{2}\sqrt{1 - 4x^2}
Substituting this back:
∫sin⁡−12x dx=xsin⁡−12x−(−121−4x2)+C\int \sin^{-1} 2x \text{ d}x = x \sin^{-1} 2x - \left( -\frac{1}{2}\sqrt{1 - 4x^2} \right) + C
=xsin⁡−12x+121−4x2+C= x \sin^{-1} 2x + \frac{1}{2}\sqrt{1 - 4x^2} + C

答案

xsin⁡−12x+121−4x2+Cx \sin^{-1} 2x + \frac{1}{2} \sqrt{1 - 4x^2} + C

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