Question

Use substitution method to solve for
y=3/2x-1
y=4x+4
The correct answer is (-2,-4) but I ended up with 8/3x=-5 ....

Answer 1

Is the second equation supposed to say \(y=4x+4\)?

Answer 2

Yes

Answer 3

Okay. It doesn't matter which equation you substitute into which, so I'll just take the first one.
\[y=\frac{3}{2}x-1\]
You can solve for \(x\), or leave it alone. I'll leave it alone. Plug it into the second equation:
\[y=4x+4~~\implies~~\frac{3}{2}x-1=4x+4\]
Good so far?

Answer 4

So far so good

Answer 5

Okay, now you solve for \(x\):
\[\begin{align*}
\frac{3}{2}x-1&=4x+4\\
\frac{3}{2}x-4x&=4+1\\
\left(\frac{3}{2}-4\right)x&=5\\
\left(\frac{3}{2}-\frac{8}{2}\right)x&=5\\
-\frac{5}{2}x&=5\\
x&=-\frac{2}{5}\times5\\
x&=-2
\end{align*}\]
You can easily find \(y\) now.