In order to solve the following system of equations by subtraction, which of the following could you do before subtracting the equations so that one variable will be eliminated when you subtract them?

4x-2y=7
3x-3y=15

A. Multiply the top equation by 3 and the bottom equation by 4.
B. Multiply the top equation by 15 and the bottom equation by 7.
C. Multiply the top equation by 1/3.
D. Multiply the top equation by -3 and the bottom equation by 2.

Question

In order to solve the following system of equations by subtraction, which of the following could you do before subtracting the equations so that one variable will be eliminated when you subtract them?

4x-2y=7
3x-3y=15

A. Multiply the top equation by 3 and the bottom equation by 4.
B. Multiply the top equation by 15 and the bottom equation by 7.
C. Multiply the top equation by 1/3.
D. Multiply the top equation by -3 and the bottom equation by 2.

anonymous · Answer

D

aravindg · Answer

The idea is to make coefficient of x or y's same. Think of the option that helps you do that.

anonymous · Answer

how do i make coefficients the same? @AravindG

aravindg · Answer

For instance consider the first  option 

 Multiply the top equation by 3 :

(4x-2y=7)3=12x-6y=21

Multiply bottom equation by 4.

(3x-3y=15)4=12x-12y=60

Notice that we got coefficients of x as same. So when we subtract them x terms get eliminated.