# Math Help - simultaneous equations, 3 unknowns

1. ## simultaneous equations, 3 unknowns

Hey, need some help with the methodology involved in solving simultaneous equations with three unknowns.

I1 = I2 + I3
8I1= 3I3
3I1+5I2=3.4

cheers.

2. Originally Posted by clayson
Hey, need some help with the methodology involved in solving simultaneous equations with three unknowns.

I1 = I2 + I3
8I1= 3I3
3I1+5I2=3.4

cheers.
First rearrange your second two equations to get them with respect to $I1$

$8I1 = 3I3$, therefore $I3 = \frac{8}{3}I1$

For the second one, do the same:

$3I1 + 5I2 = 3.4$, $5I2 = 3.4 - 3I1$, so $I2 = \frac{3.4 - 3I1}{5}$.

Now put these values of $I2$ and $I3$ in to your first equation, you now have an equation in terms of just $I1$.

Solve this and then put your value for $I1$ back into the second and third equations to find all terms.