求不定积分∫e^(-2t)costdt原式=∫costdt/e^(2t)=∫d(sint)/e^(2t)=sint/e^(2t)+2∫sintdt/e^(2t)=sint/e^(2t)-2∫d(cost)/e^(2t)=sint/e^(2t)-2[cost/e^(2t)+2∫costdt/e^(2t)]=(sint-2cost)/e^(2t)-4∫costdt/e^2t...