=(1/2)∫sinx^2d(x^2)
=-cos(x^2)/2+C
13.∫sinxdx/(cosx)^6
=-∫dcosx/(cosx)^6
=1/[5(cosx)^5]+C
15.∫(sinx)^3dx
=∫(3sinx-sin3x)dx/4
=cos3x/12-3cosx/4+C
22.∫(tanx)^4(secx)^2dx
=∫(tanx)^4d(tanx)
=(tanx)^5/5+C
这 4 道题都是比较好做的,类型基本一样:
∫x * sin(x²) * dx
=∫sin(x²) * (x * dx)
=∫sin(x²) * 1/2 * d(x²)
=1/2 * ∫sin(u) * du 设 u = x²
= 1/2 * (-cosu) + C
= -1/2 * cos(x²) + C
∫sinx * dx/(cosx)^6
=∫(sinx * dx) * (cosx)^(-6)
=∫- d(cosx) * (cosx)^(-6)
=-∫u^(-6) * du 设 u = cosx
= -1/(-6+1) * u^(-5) + C
= 1/5 * u^(-5) + C
= 1/[5(cosx)^5] + C
∫sin³x * dx
=∫sinx * sin²x * dx
=∫sinx * (1 - cos²x) * dx
=∫sinx * dx - ∫sinx * dx * cos²x
=-cosx + ∫d(cosx) * cos²x 注:d(cosx) = -sinx * dx
=-cosx + ∫u² * du 设 u = cosx
=-cosx + 1/3 * u³ + C
=-cosx + cos³x/3 + C
∫(tanx)^4 * sec²x * dx
=∫(tanx)^4 * d(tanx) 注:d(tanx) = sec²x * dx
=∫u^4 * du 设 u = tanx
=u^5 /5 + C
=(tanx)^5 /5 + C