cosx/(2-cotx^2)的不定积分

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cosx/(2-cotx^2)的不定积分

cosx/(2-cotx^2)的不定积分
cosx/(2-cotx^2)的不定积分

cosx/(2-cotx^2)的不定积分
I=∫[cosx/(2-cotx^2)]dx=∫{cosx(sinx)^2/[2(sinx)^2-(cosx)^2]}dx
=∫{cosx(sinx)^2/[3(sinx)^2-1]}dx=∫{(sinx)^2/[3(sinx)^2-1]}d(sinx),
令u=sinx, 则原积分化为
I=∫[u^2/(3u^2-1)]du=(1/3)∫[(u^2-1/3+1/3)/(u^2-1/3)]du
=(1/3)∫[1+(1/3)/(u^2-1/3)]du=u/3+(1/9)∫[1/(u^2-1/3)]du
=u/3+(1/9)(√3/2)ln|(u-1/√3)/(u+1/√3)|+C
=(1/3)sinx+(√3/18)ln|(sinx-1/√3)/(sinx+1/√3)|+C.