Question

不定积分求解。救命啊……

Sinx*sin3x的不定积分怎么解？详细过程呢…

Answer 1

Sinx*sin3x=1/2*(cos(x-3x)-cos(x+3x)
=1/2(cos2x-cos4x)
S Sinx*sin3xdx
=1/2*S(cos2x-cos4x)
=1/2*1/2*sin2x-1/2*1/4*sin4x+c
=-1/8*sin4x+1/4*sin2x +c

Answer 2

sinxsin3x=(1/2)[cos[(3x-x)]-cos[(3x+x)]]=(1/2)[cos2x-cos4x}
∫sinxsin3xdx=∫(1/2)[cos2x-cos4x]dx=(1/4)sin4x-(1/8)(sin4x)+C