MATLAB,怎么求符号函数的导数在某一点的值?比如,一函数y=sin(x),那...答:>> syms x L vpa(subs(diff(sin(x)),x,L))ans = cos(L)>> syms x vpa(subs(diff(sin(x)),x,5))ans = 0.28366218546322624627364916705119 >> syms x subs(diff(sin(x)),x,5)ans = 0.2837 vpa(式子, 变量 , 默认值20)vpa是用来设置结果精度的,可以不需要。