By integration property
∫a0f(x)dx=∫a0f(a−x)dx
∴I=∫π/20logsin(π/2−x)dx=∫π/20logcosxdx
∴2I=∫π/20(logsinx+logcosx)dx
2I=∫π/20log(sinxcosx)dx.
=∫π/20logsin2x2dx.
=∫π/20logsin2xdx−∫π/20log2dx.
Substitute 2x=t in the 1st. ∴2dx=dt and limits become 0 to π.
∴2I=12∫π0logsintdt−[xlog2]π/20
Now apply Prop. Vi in 1st. ∵f(2a−x)=f(x).
2I=12.2∫π/20logsintdt−π2log2
or 2I=∫π/20logsinxdx−(π/2)log2, by prop. Ior 2I=I+π2log12
∴I=∫π/20logsinxdx=∫π/20logcosxdx=π2log12