# solving two equations with 4 unknowns

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Hello all,

Can you please tell me how can I solve 4 equations with 2 unknowns in MATLAB?

##### 3 Comments

Sean de Wolski
on 7 Jul 2011

### Accepted Answer

Sean de Wolski
on 7 Jul 2011

Edited: Walk before you run:

syms x y

results = solve('3*x+y=9','x-7*y=-3',x,y)

results.x

results.y

look at

doc solve

to learn more.

##### 5 Comments

### More Answers (2)

Walter Roberson
on 16 Jul 2011

syms T12 T11 T21 T22 R11 R12 R21 R22 H21_1 H21_2 H12_1 H12_2 lambda beta alpha

solve((T21.^2.* H21_1.^2+beta^(-1) ).* R11.^2+(T21.* T2_2.* H21_1.* H21_2 ) .*R11.* R12 - (lambda*alpha).*((R21.^2.* H12_1.^2+lambda).* T11.^2+(R21.* R22 H12_1.* H12_2 ).* T11.* T12 ), lambda)

Notice that the A=B form you had has been replaced by A-B, which solve will interpret as indicating that (A-B)=0 is desired.

In the second line, replace the "lambda" at the end by the name of the variable you want to solve for. As you only have one equation, you can only effectively solve for a single variable.

##### 0 Comments

SooShiant
on 20 Feb 2014

Combine 2 equation to gain 1 then use this way:

Here is a simple example which you can change the equation and range and solve yours. The equation is 12x+9y+7z-60=0 where x,y,z are integers varies 0 to 10:

x=[0:1:10];

y=[0:1:10];

z=[0:1:10];

[X,Y,Z]=ndgrid(x,y,z);

F=12.*X+9.*Y+7.*Z-60;

idx=find(F==0);

[X(idx(:)),Y(idx(:)),Z(idx(:))];

Equations of this type are known as Diophantine equations.

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