# Write a system of linear equations with exactly one solution

Introduction Sometimes graphing a single linear equation is all it takes to solve a mathematical problem. This is often the case when a problem involves two variables.  Manipulating expressions with unknown variables Video transcript In the last video, we saw what a system of equations is. And in this video, I'm going to show you one algebraic technique for solving systems of equations, where you don't have to graph the two lines and try to figure out exactly where they intersect.

This will give you an exact algebraic answer. And in future videos, we'll see more methods of doing this. So let's say you had two equations. One is x plus 2y is equal to 9, and the other equation is 3x plus 5y is equal to Now, if we did what we did in the last video, we could graph each of these.

You could put them in either slope-intercept form or point-slope form. They're in standard form right now. And then you could graph each of these lines, figure out where they intersect, and that would be a solution to that. But it's sometimes hard to find, to just by looking, figure out exactly where they intersect.

So let's figure out a way to algebraically do this. And what I'm going to do is the substitution method. I'm going to use one of the equations to solve for one of the variables, and then I'm going to substitute back in for that variable over here.

So let me show you what I'm talking about. So let me solve for x using this top equation. So the top equation says x plus 2y is equal to 9. I want to solve for x, so let's subtract 2y from both sides of this equation.

So I'm left with x is equal to 9 minus 2y.

## Systems of Linear Equations

This is what this first equation is telling me. I just rearranged it a little bit. The first equation is saying that. So in order to satisfy both of these equations, x has to satisfy this constraint right here. So I can substitute this back in for x.

## Distance Formula

We're saying, this top equation says, x has to be equal to this. Well, if x has to be equal to that, let's substitute this in for x. So this second equation will become 3 times x. And instead of an x, I'll write this thing, 9 minus 2y.

That's why it's called the substitution method. I just substituted for x. And the reason why that's useful is now I have one equation with one unknown, and I can solve for y. So let's do that 3 times 9 is Add the negative 6y plus the 5y, add those two terms. You have let's see, this will be-- minus y is equal to Let's subtract 27 from both sides.

And you get-- let me write it out here. So let's subtract 27 from both sides. The left-hand side, the 27's cancel each other out. And you're left with negative y is equal to 20 minus 27, is negative 7.

And then we can multiply both sides of this equation by negative 1, and we get y is equal to 7.The system of equations 2x+y=0 and x-y=0 has exactly one solution since the slopes of the lines are different, i.e. the determinant is non-zero. The solution is of course (0,0).

Section Linear Systems with Two Variables. A linear system of two equations with two variables is any system that can be written in the form. Systems of Linear Equations. A Linear Equation is an equation for a line.

A System of Linear Equations is when we have two or more linear equations working together. Example: Here are two linear equations: 2x + y = 5 −x + y = 2: Together they are a system of linear equations.

Write one of the equations so it is in the style "variable. Deterministic modeling process is presented in the context of linear programs (LP). LP models are easy to solve computationally and have a wide range of applications in diverse fields.

This site provides solution algorithms and the needed sensitivity analysis since the solution to a practical problem is not complete with the mere determination of the optimal solution.

Linear equations represent lines (or planes, etc., but essentially we are interested in lines for this question). If two lines are coincident (i.e. the same line), then they intersect at all points along the line - that is, infinitely many points and hence infinitely many solutions.

· Graph a system of linear equations on the coordinate plane and identify its solution. The system has one solution. C) The system has two solutions. D) The system has infinite solutions. While graphing systems of equations is a useful technique, relying on graphs to identify a specific point of intersection is not always an accurate.

Consistent and Inconsistent Systems of Equations | Wyzant Resources