∫x/(3+4x+x^2)^1/2dx
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∫x/(3+4x+x^2)^1/2dx
∫x/(3+4x+x^2)^1/2dx
∫x/(3+4x+x^2)^1/2dx
∫[x/√(3+4x+x^2)]dx
=∫{x/√[(x^2+4x+4)-1]}dx
=∫{x/√[(x+2)^2-1]}dx
=∫{[(x+2)-2]/√[(x+2)^2-1]}d(x+2).
令x+2=1/sinu,则:d(x+2)=[cosu/(sinu)^2]du,
∴∫[x/√(3+4x+x^2)]dx
=∫{(1/sinu-2)/√[1/(sinu)^2-1]}[cosu/(sinu)^2]du
=∫[(1/sinu-2)/(cosu/sinu)][cosu/(sinu)^2]du
=∫[(1/sinu-2)/sinu]du
=∫[(1-2sinu)/(sinu)^2]du
=∫[1/(sinu)^2]du+2∫[1/(sinu)^2]d(cosu)
=-cotu+2∫{1/[(1-cosu)(1+cosu)]}d(cosu)
=-cosu/sinu+∫{(1-cosu+1+cosu)/[(1-cosu)(1+cosu)]}d(cosu)
=-cosu/sinu+∫[1/(1+cosu)]d(cosu)+∫[1/(1-cosu)]d(cosu)
=-(x+2)√[1-(sinu)^2]+ln|1+cosu|-ln|1-cosu|+C
=-(x+2)√[1-1/(x+2)^2]+ln|(1+cosu)/(1-cosu)|+C
=-√[(x+2)^2-1]+ln|(1+cosu)^2/[1-(cosu)^2]|+C
=-√(x^2+4x+3)+ln|(1+cosu)^2/(sinu)^2|+C
=-√(x^2+4x+3)+2ln|(1+cosu)/sinu|+C
=-√(x^2+4x+3)+2ln|{1+√[1-(sinu)^2]}(x+2)|+C
=-√(x^2+4x+3)+2ln|(x+2)+(x+2)√[1-1/(x+2)^2]|+C
=2ln|x+2+√(x^2+4x+3)|-√(x^2+4x+3)+C.