复合函数求导先对sin函数求导,再对根号x/3求导
y = sin√(x/3) y' = cos√(x/3) * [√(x/3)]' = cos√(x/3) * (1/2)*(x/3)^(-1/2)*(x/3)'= √3cos√(x/3)/(6√x)
y = sin (sqrt(x/3))y'=cos(sqrt(x/3))·(sqrt(x/3))'=cos(sqrt(x/3))·(1/2)·((x/3)^(-1/2))=(1/2)(sqrt(3/x))·cos(sqrt(x/3))