设2^x=t
ln2^x=xln2=lnt
x=lnt/ln2
dx=1/(tln2)
∫1/(2^x+7)dx
=∫1/(t+7)*1/(tln2)dt
=1/ln2∫dt/(t(t+7))
=1/ln2∫dt[1/7t-1/7(t+7)]
=1/7ln2∫dt[(1/t-1/(t+7)]
=1/7ln2∫dt/t-1/7ln2∫dt/(t+7)
=lnt/7ln2-ln(t+7)/7ln2+C
=ln[t/(t+7)] /7ln2+C
=ln[2^x/(2^x+7)]/7ln2+C
设2^x=t
ln2^x=xln2=lnt
x=lnt/ln2
dx=1/(tln2)
∫1/(2^x+7)dx
=∫1/(t+7)*1/(tln2)dt
=1/ln2∫dt/(t(t+7))
=1/ln2∫dt[1/7t-1/7(t+7)]
=1/7ln2∫dt[(1/t-1/(t+7)]
=1/7ln2∫dt/t-1/7ln2∫dt/(t+7)
=lnt/7ln2-ln(t+7)/7ln2+C
=ln[t/(t+7)] /7ln2+C
=ln[2^x/(2^x+7)]/7ln2+C