∫√(9-x^2)dx
令x=3sint dx=3cost dt
√(9-x^2)=3cost
原式=∫3cost *3cost dt
=9∫cos^2 t dt
=9/2∫(cos2t +1) dt
=9/2∫cos2t dt +9/2∫dt
=9sin2t /4 +9t/2 +C
自己代回来吧