令x=√2sint
则原式=∫(π/4→π/2)√2cost*√2costdt
=∫(π/4→π/2)2cos^2(t)dt
=∫(π/4→π/2)(cos(2t)+1)dt
=sin(2t)/2|(π/4→π/2)+t|(π/4→π/2)
=0-1/2+π/4=π/4-1/2