Solving quadratic equations

Question

Given y=-x²-x+15 (from graph)

and 10=x²+x

Showing your method clearly, use your graph to solve the following equations. 

Answer 1

Gwyneth,

If the second equation, 10=x²+x, is multiplied by -1,it becomes -10=-x²-x. That means the first two terms of the first equation, -x²-x, can be replaced by -10, so y = -10 +15 = 5.

Graph the first equation, y=-x²-x+15, with the y=5 equation and find the intersections to solve the simultaneous equations.

I show the intersections at (2.7015, 5) and (-3.7015, 5).

I hope this helps!

Answer 2

These two graphs will be drawn on the same coordinate system.  All you have to do is look for the point(s) of intersection.