Example of two variables one degree equation

Question:

Given: x + 3y = 9 ...equation1

and 3x + 6 = 15 ...equation2

solve for x and y.

Solution:

because the equation2 has only one variable x, so we solve equation2 first to get the value of x.

3x + 6 = 15

move the number to the right side of the equation

3x = -6 + 15 = 9

x = 9/3 = 3

substitute x = 3 into equation1

x + 3y = 9

3 + 3y = 9

3y = 9 - 3 = 6

y = 6/3 = 2

so the solution is x = 3 and y = 2

Use the substitution method to solve the two variables equations. Because the equation2 has only one variable x, make the equation2 into the standard form ax = b. the value of x is b/a. Substitute the value os x into equation1 to get an equation which has only varianle y. make the equation into the standard form cy = d, then y = d/c. Check if the valurs of x and y satisfy original equations.