∫[π^2,0]cos√xdx=?
1个回答

∫[π^2,0]cos√xdx

换元法

设t=√x,则x=t^2

=∫(0→π)cost dt²

=2∫(0→π)tcost dt

=2∫(0→π)tdsint

=2tsint - ∫(0→π)sintdt

=2tsint + cost |(0→π)

=-2