2)
y=log(x)としたら
x=exp(y)
dy=dx/x=dx/exp(y)

x:0→1　;　y:∞→0
∫[0,1]log(x)dx
=∫[∞→0]yexp(-y)dy
[-yexp(-y)][∞→0]-∫[∞→0]-exp(-y)dy

？？？ヽ(`Д´)ﾉ