Question

If you were to solve the following system by substitution, what would be the best variable to solve for and from what equation?

2x+6y=9
3x-12y=15


A. y, in the first equation
B. x, in the second equation
C. x, in the first equation
D. y, in the second equation

Answer 1

Answer: B. x, in the second equation

Explanation:

The given system :

`2x+6y=9...................(1)\\\\3x-12y=15.........................(2)`

To apply the substitution method , first we need to select the best variable and a equation which is easy to simplify.

From the given system equation (2) have all the numbers which are multiples of 3.

Then we divide 3 on both sides of equation (2), we get

`x-4y=5\\\\\Rightarrow\ x=4y+5`

Therefore, the best variable to solve for and from what equation is x, in the second equation.