You need to use one equation in order to solve for the other. Here's an example x+y=20 x-y=10 Now, solve for one of the variables in either equation. It does not matter which. x-y=10 Add y to both sides in order to cancel it out. x=10+y Now, plug "10+y" in for the x variable in one of the first two equations in order to find y. x=y=20 The original 10+y+y=20 This is what it would look like after plugging in x. Now, combine like terms. 10+2y=20 Next, cancel out the 10 by subtracting it from both sides. 2y=10 Now cancel out the 2 by dividing each side by two. y=5 You will now plug "5" in for why in one of the original formulas. x+y=20 The original x+5=20 After plugging in "5" for y. Now cancel out the 5 by subtracting 5 from each side. x=15 Now your answer is (15,5)

No... When given two or more equations with two or more variables, use on of the equations to find an equation for one of the variables, then plug that into another equation. x + b = 2 ...(1) 3x + 5b = 8 ...(2) Using (1), we see that x = 2 - b Plug that into (2), and you get: 3(2 - b) + 5b = 8 --> 6-3b + 5b = 8 --> 2b = 2 --> b = 1 Use that in equation (1), and you get: x + 1 = 2 --> x = 1 At no point are you setting variables equal to zero. If the variables happen to come out to be zero, it's just a coincidence. These can be solved easily with a matrix if you want to avoid doing it by hand.

Need example. Maths in the word form makes my head hurt.

Assuming I'm understanding the question, there's no definitive answer to the question you posed. You just need to observe how the problem looks. And are we solving a linear [I]system[/I] of equations, or just a single equation?

I don't know, do I look like the God of Math to you?!?