Question

Solve the linear system of equations using the linear combination method

4x +5y=7
y=3x+9
Enter your answers in the boxes.
x=
y=​

Answer 1

x = -2

y = 3

Explanation:

Write the system the following way:

4x + 5y = 7

-3x +y = 9

we need to eliminate one unknown by multiplying one equation for a suitable number in such a way that when we add the equations one unknown is eliminated.

If we multiply the second eq. by -5 the y is eliminated

4x + 5y = 7

15x -5y = -45

add the equations

19x = -38 ===> x = -38/19 ===> x = -2

Now replace this value in any equation to get y. For example, in 1st one.

4(-2) + 5y = 7 ===> -8 +5y = 7 ===> 5y = 7+8 ===> 5y = 15 ===> y = 15/5 ===>

y=3