Answer :
Do the change of variable [tex]u=\cos(t)\rightarrow du=-\sin(t)dt[/tex]
Then [tex]\int\2cos^2(t)\sin(t)dt=-2\int u^2du=-\frac{u^3}3=-\frac{2}3\cos^3(t)[/tex]
Then [tex]\int\2cos^2(t)\sin(t)dt=-2\int u^2du=-\frac{u^3}3=-\frac{2}3\cos^3(t)[/tex]
