Answer:
y=5
Step-by-step explanation:
Any equation that's y=c (or any other constant) is a horizontal line. Imagine a parabola and a horizontal line plotted on a graph.
There are three possibilities of where the horizontal line can be:
It may not touch the parabola at all,
It may touch the parabola at one specific point (it's a tangent line)
Or it may touch the parabola at two points (it's a secant line)
The question prompt tells us that the horizontal line y=c touches the parabola at exactly one point; so for it not to touch two points it has to touch the parabola at the vertex point, right?
If we graph the parabola (or we could just look at the equation and it should be intuitive), we find out that the y-intercept is 5. In other words the point where the function reaches its maximum value (maxima) is at y=5.
For this reason, the value of c is 5 since if it was any value below that it would touch more than one point and if it was above it it wouldn't touch any point.
Here's an image so that it'll be a bit clearer hopefully:
Good luck!
