Question

If you were to use the substitution method to solve the following system, choose the new equation after the expression equivalent to x from the second equation is substituted into the first equation.
3x + 2y = –21
x – 3y = 4

a. 3(–3y + 4) + 2y = –21
b. 3x + 2(3y + 4) = –21
c. 3(3y + 4) + 2y = –21
d. 3x + 2(–3y + 4) = –21

Answer 1

You would first isolate x in the second equation.

\( \color{Black}{\Rightarrow x = 4 + 3y}\)

Now you will replace \(x\) with \(4 + 3y\).

Answer 2

\( \color{Black}{\Rightarrow 3(4 + 3y) + 2y = -21}\)

Answer 3

According to the commutative property you can write 4 + 3y as 3y + 4 too

\( \color{Black}{\Rightarrow 3(3y + 4) + 2y = -21}\)