例2计算cos60°30的近似值 解:设f(x)=cosx→∫(x)=-sinx(x为弧度) △y 元 3 360 √3 f(t2 3 2 cos60°30′=c0s(z+f 3360 ≈f()+f(x) √3z 22300≈0.4924例2 计算cos6030的近似值 解: 设f(x)=cosxf (x)= −sinx (x为弧度) 3 0   x = 360  x = 2 1 ) 3  ( =  f 2 3 ) 3 ( = −  f ) 3 360 cos60 30 cos(     = + 360 ) 3 ) ( 3 (     f + f  2 360 3 2 1  = − 0.4924