Question

matlab中如何以x为自变量解三角函数方程组

我写的代码是
[y,z]=solve('85+45*cos(y)+50*cos(z)=35*cos(x)','45*sin(y)+50*sin(z)=35*sin(x)','x')
但是解不出来
请问是怎么回事呢

Answer 1

解方程f（x）=0的代码是：
solve('f(x)=0','x')或solve('f(x)','x')
变量缺省时，默认变量为x
方程组f(x,y)=0，g(x,y)=0的代码是
solve('f(x,y)=0','g(x,y)=0','x,y')
缺省变量时，默认变量为x，y
你要是只以x为变量是解不出来的

还有我看你代码的意图是以y，z为变量，以x为常量，用x表示y与z吧。
在方程组中只有变量与常量，是没有自变量的。

追问

我想解的是85+45*cos(y)+50*cos(z)=35*cos(x)和45*sin(y)+50*sin(z)=35*sin(x)这两个方程，y、z并不显含x，那具体该怎么写呢？

追答

你要的是不是这个

[y,z]=solve('85+45*cos(y)+50*cos(z)=35*cos(x)','45*sin(y)+50*sin(z)=35*sin(x)','y,z')

追问

出现了一个zll还有warning，这是怎么回事呢？

追答

y =

atan(-5/9/(11328800*sin(x)^2+11520000)*(633080*sin(x)*cos(x)+8963080*sin(x)+7930160*sin(x)^3+40*(250493929*sin(x)^2*cos(x)^2+326963762160*sin(x)^2*cos(x)+131125592108*sin(x)^4*cos(x)-7762182169*sin(x)^2+14285786732*sin(x)^4+39304648516*sin(x)^6+196169500800*cos(x)+18149500800)^(1/2))+7/9*sin(x),1/18*(-3757-1190*sin(x)/(11328800*sin(x)^2+11520000)*(633080*sin(x)*cos(x)+8963080*sin(x)+7930160*sin(x)^3+40*(250493929*sin(x)^2*cos(x)^2+326963762160*sin(x)^2*cos(x)+131125592108*sin(x)^4*cos(x)-7762182169*sin(x)^2+14285786732*sin(x)^4+39304648516*sin(x)^6+196169500800*cos(x)+18149500800)^(1/2))-490*sin(x)/(11328800*sin(x)^2+11520000)*(633080*sin(x)*cos(x)+8963080*sin(x)+7930160*sin(x)^3+40*(250493929*sin(x)^2*cos(x)^2+326963762160*sin(x)^2*cos(x)+131125592108*sin(x)^4*cos(x)-7762182169*sin(x)^2+14285786732*sin(x)^4+39304648516*sin(x)^6+196169500800*cos(x)+18149500800)^(1/2))*cos(x)+1813*cos(x)+686*sin(x)^2*cos(x))/(49*sin(x)^2+240))

atan(-5/9/(11328800*sin(x)^2+11520000)*(633080*sin(x)*cos(x)+8963080*sin(x)+7930160*sin(x)^3-40*(250493929*sin(x)^2*cos(x)^2+326963762160*sin(x)^2*cos(x)+131125592108*sin(x)^4*cos(x)-7762182169*sin(x)^2+14285786732*sin(x)^4+39304648516*sin(x)^6+196169500800*cos(x)+18149500800)^(1/2))+7/9*sin(x),1/18*(-3757-1190*sin(x)/(11328800*sin(x)^2+11520000)*(633080*sin(x)*cos(x)+8963080*sin(x)+7930160*sin(x)^3-40*(250493929*sin(x)^2*cos(x)^2+326963762160*sin(x)^2*cos(x)+131125592108*sin(x)^4*cos(x)-7762182169*sin(x)^2+14285786732*sin(x)^4+39304648516*sin(x)^6+196169500800*cos(x)+18149500800)^(1/2))-490*sin(x)/(11328800*sin(x)^2+11520000)*(633080*sin(x)*cos(x)+8963080*sin(x)+7930160*sin(x)^3-40*(250493929*sin(x)^2*cos(x)^2+326963762160*sin(x)^2*cos(x)+131125592108*sin(x)^4*cos(x)-7762182169*sin(x)^2+14285786732*sin(x)^4+39304648516*sin(x)^6+196169500800*cos(x)+18149500800)^(1/2))*cos(x)+1813*cos(x)+686*sin(x)^2*cos(x))/(49*sin(x)^2+240))

z =
也是一个很长的数，超过字数了，打不上
这是我算的，没有你说的呀

追问

那请问你安装的matlab版本是2011b么？会不会是我的版本的问题？

追答

我的是matlab 7 ，这个应该不会吧