MHB Can Complex Numbers Solve This Linear System?

[toni07]

$$\mathbb C: (1+i)x + 2y = 3, 3x + (1i)y = 2i$$

I don't know how to go about this, am I supposed to do addition of complex number? Please help.

 

[MarkFL]

One way to proceed would be to multiply the second equation by $2i$, and then add the two equations:

$$(1+i)x+2y=3$$

$$6ix-2y=-4$$

Then you will have eliminated $y$ and can solve for $x$, after which you may substitute for $x$ into either equation to determine $y$.

 

[toni07]

One way to proceed would be to multiply the second equation by $2i$, and then add the two equations:

$$(1+i)x+2y=3$$

$$6i-2y=-4$$

Then you will have eliminated $y$ and can solve for $x$, after which you may substitute for $x$ into either equation to determine $y$.

I am not supposed to use Gaussian elimination.

 

[MarkFL]

I thought Gaussian elimination involved an augmented matrix. If you are not to use any type of elimination then use substitution instead.

 

[eddybob123]

Since this has two equations and two variables, it's easy to apply Cramer's Rule, since the determinant of a 2x2 matrix $\begin{bmatrix}a&b\\c&d \end{bmatrix}$ is just $ad-bc$

 

[HallsofIvy]

I am not supposed to use Gaussian elimination.

It would have helped if you had told us that!

In any case "complex numbers", as far as algebra is concerned, are just numbers. Any method that you could use with real coefficients works with complex coefficients.

If you are not allowed to use the easiest method (Gaussian elimination) you could use Cramer's rule, as eddybob123 suggested:
x= \dfrac{\left|\begin{array}{ccc}3 & 2 \\ 2i & 2i\end{array}\right|}{\left|\begin{array}{ccc}1+i & 2 \\ 3 & i \end{array}\right|}
y= \dfrac{\left|\begin{array}{ccc}1+i & 3 \\ 3 & 2i\end{array}\right|}{\left|\begin{array}{ccc}1+i & 2 \\ 3 & i \end{array}\right|}

(Editted thanks to eddybob123.)

 

[eddybob123]

I'm sure you meant y on the second equation!

 

[toni07]

It would have helped if you had told us that!

In any case "complex numbers", as far as algebra is concerned, are just numbers. Any method that you could use with real coefficients works with complex coefficients.

If you are not allowed to use the easiest method (Gaussian elimination) you could use Cramer's rule, as eddybob123 suggested:
x= \dfrac{\left|\begin{array}{ccc}3 & 2 \\ 2i & 2i\end{array}\right|}{\left|\begin{array}{ccc}1+i & 2 \\ 3 & i \end{array}\right|}
x= \dfrac{\left|\begin{array}{ccc}1+i & 3 \\ 3 & 2i\end{array}\right|}{\left|\begin{array}{ccc}1+i & 2 \\ 3 & i \end{array}\right|}

I thought I could figure it out. What if I don't want to use Cramer's rule.

 

[MarkFL]

$$(1+i)x+2y=3$$

$$6ix-2y=-4$$

Solve one of these equations for $2y$ and then substitute that into the other equation and solve for $x$.

 

[DimsVS]

$$\mathbb C: (1+i)x + 2y = 3, 3x + (1i)y = 2i$$

I don't know how to go about this, am I supposed to do addition of complex number? Please help.

Online service - linear system to complex numbers

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