Question

怎么用matlab求解cos(x)-x*sin(x)=0并画出y=cos(x)-x*sin(x)的图像？在线等，急用！！

Answer 1

ezplot('cos(x)-x*sin(x)') %画出图像
fzero('cos(x)-x*sin(x)',x0) %x0是你根据图像猜的根，函数返回该值附近的零点

ezplot默认的范围是[-2*pi,2*pi]，是有4个零点。你分别猜一下就可以了。或者可以写个for循环

for k=[-3,-1,1,3]
fzero('cos(x)-x*sin(x)',k)
end

Answer 2

syms x y
z=y-cos(x)+x*sin(x)==0
ezplot(z)
solve(z,x)

会提示显式解无法求出。试试fzero函数求零点

追问

可以具体点吗？

追答

用help fzero，这个函数专门用来求零点的。如果不行，你就用数值方法求解方程。
>> help fzero
fzero Single-variable nonlinear zero finding.
X = fzero(FUN,X0) tries to find a zero of the function FUN near X0,
if X0 is a scalar. It first finds an interval containing X0 where the
function values of the interval endpoints differ in sign, then searches
that interval for a zero. FUN is a function handle. FUN accepts real
scalar input X and returns a real scalar function value F, evaluated
at X. The value X returned by fzero is near a point where FUN changes
sign (if FUN is continuous), or NaN if the search fails.

追问

只能输出一个解，一共有四个，请问怎么办啊

Answer 3

%按楼上数值解吧
func=@(x)(cos(x)-x.*sin(x));

x_v=fsolve(func,2);
xdata=-10:0.1:10; plot(xdata,func(xdata))