Question

求(3x^2+1)cosnx的原函数,

Answer 1

=（3xx+1）sinnx/n-(积分号)6xsinnx/n=(3xx+1)sinnx/n+6xcosnx/(nn)-(积分号)6cosnx/(nn)=sinnx*((3xx+1)/n-6/nnn)+cosnx*6x/nn+c;