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不定积分,这两题怎么算,给过程
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9. ∫ xf(x) dx = arcsinx + C
xf(x) = (arcsinx)' = 1/√(1-x^2), x 不可能等于 0
f(x) = 1/[x√(1-x^2)],
∫ [1/f(x)] dx = ∫ x√(1-x^2) dx = -(1/2) ∫ √(1-x^2) d(1-x^2)
= -(1/3)(1-x^2)^(3/2) + C
10. f(x) = (xlnx)' = 1+lnx, f'(x) = 1/x,
∫ xf''(x) dx = ∫ x df'(x) = xf'(x) - ∫ f'(x) dx = xf'(x) - f(x) + C
= 1 - (1+lnx) + C = C - lnx
xf(x) = (arcsinx)' = 1/√(1-x^2), x 不可能等于 0
f(x) = 1/[x√(1-x^2)],
∫ [1/f(x)] dx = ∫ x√(1-x^2) dx = -(1/2) ∫ √(1-x^2) d(1-x^2)
= -(1/3)(1-x^2)^(3/2) + C
10. f(x) = (xlnx)' = 1+lnx, f'(x) = 1/x,
∫ xf''(x) dx = ∫ x df'(x) = xf'(x) - ∫ f'(x) dx = xf'(x) - f(x) + C
= 1 - (1+lnx) + C = C - lnx
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