Question

If 3x-1=11,what is the value of x^2+x

Answer 1

We can set the 2nd equation to y that way we have something to solve for
$\left \{ {{3x-1=11} \atop {x^2+x=y}} \right.$
First we solve our first equation by moving the one to the other side
$3x=12$
Then we divide by 3 on each side
$x=4$
So now we can plug 4 into the x's of the 2nd equation
$4^2+4=y\\ 16+4=y\\ 20=y$