# One Equation, Two Variables

Pro Problems > Math > Algebra > Equations > Systems of Equations > Non-Linear## One Equation, Two Variables

Usually we say that if we have two variables, we need two equations to solve, and if we have three variables, we need three equations to solve. This is not 100% true, however, and the problem below is a good example of a single equation in two variables which produce a single ordered pair solution.

Solve for the ordered pair (x,y) such that x^{2} + y^{2} - 2x + 4y = -5

## Solution

In order to make it feasible for teachers to use these problems in their classwork, no solutions are publicly visible, so students cannot simply look up the answers. If you would like to view the solutions to these problems, you must have a Virtual Classroom subscription.## Similar Problems

### Cubic and Linear

Find all ordered pairs (x,y) which solve the following system of equations:

x^{3} + 12xy^{2} = 7x^{2}y

x + y = 20

### X and Y System

Find all ordered pairs (x,y) which solve the following non-linear system of equations.

x(x - 2y) - 4 = 2y(x - 2y)

x + 2y = 10

### Quadratic System

Find all ordered pairs (x, y) such that the following two equations are true:

x^{2} - 4y^{2} = 108

x = 18 - 2y

### Quadratic System

Solve for m and n.

(m + n)^{2} - 10(m + n) + 24 = 0

(m - n)^{2} + 6(m - n) + 8 = 0

### System with a Product

Find all ordered pairs (x, y) such that

2x + xy + y = 18

x - y = 2

### System with Radical

The sum of two numbers is seven times the difference between three times the second number and twice the first number. If the second number is subtracted from the first, the result is the square root of the first. Find all possible values for the first number.

### X and Y Quadratics

Find the sum of x and y, if the following are true:

(x + 2)(x - 1) = (y - 12)(y + 3)

(x + 1)(x + 3) = (y - 5)(y - 7)

### Sum and Product System

The sum of a number and twice another number is ten less than the product of the numbers. The sum of the numbers is ten. What are all possible numbers that satisfy these criteria?

### To Sum It Up

I have picked three positive integers for the lottery, as follows: The sum of my numbers is 54. The sum of my numbers, plus the sum of two of my numbers, is 84. The sum of the squares of my numbers is 1034. What are the three integers?

### Mary and Laura's Cookies

Mary and Laura Ingalls each receive a cookie. Because they are thoughtful children, they want to share with their little sister Carrie. Because their math skills aren't very advanced, they each eat half of a cookie, but then realize that leaves a full cookie for Carrie.

How much should each girl eat in order to share equally among the three sisters?