设 x = cos(4t),
则 dx = -sin(4t)*4dt.
sin(4t)dt = (-1/4)dx.
Ssin(4t)[sec(cos(4t))]^2dt = S[sec(x)]^2(-1/4)dx
= (-1/4)S [sec(x)]^2 dx
= (-1/4) tan(x) + C
= (-1/4) tan[cos(4t)] + C
其中,C为任意常数,S表示积分符号.
求用替代法则（substitution rule)来解决一道数学积分题
设 x = cos(4t),
则 dx = -sin(4t)*4dt.
sin(4t)dt = (-1/4)dx.
Ssin(4t)[sec(cos(4t))]^2dt = S[sec(x)]^2(-1/4)dx
= (-1/4)S [sec(x)]^2 dx
= (-1/4) tan(x) + C
= (-1/4) tan[cos(4t)] + C
其中,C为任意常数,S表示积分符号.