Y=-x^2-4x+23 and 2x+y=15 what is the solution

This is a system of equations, meaning you find the value of one variable and substitute it into the other equation

if y=-x^2-4x+23 we can put that into the second equation for y

This gives us 2x + (-x^2-4x+23) = 15

Lets simplify this and set it equal to 0 by moving the 15 over

-x^2-2x+8=0

This gets us x=-4, 2

Lets try plugging both those back into our first equation and see what value of y we get

y = - (-4^2) - 4 (-4) + 23; y=23

y = - (2^2) - 4 (2) + 23; y=11

So you get two sets of solutions

(-4,23) and (2,11)