(2)VG2-y2 解令x= asin t,有√a2-x2= a cos t,d= a cos tdt 且x=0,t=0; dx=2 acost. a cos tdt=a cos tdt 0 0 1+cos 2t (2t +sin 2t) 4 注1由几何意义知,此定积分a2-x即为圆7 2 2 解 令 有 sin , cos , cos x a t a x a t dx a tdt = − = = 0, 0; , 2 x t x a t  且 = = = = 2 2 0 (2) a a x dx −  2 2 2 2 0 0 a t a tdt a tdt cos cos cos   =  =   2 2 0a a x dx −  2 20 1 cos 2 2 t a dt  + =  2 2 1 2 (2 sin 2 ) 4 4 0 a t t a  = + =  注1 由几何意义知, 此定积分 即为圆 2 2 0a a x dx − 