Test 7 Section 3 - #12 (page 772)

The question tells us that the perimeter of rectangle PQRS is 10.  A quick look at the graph tells us that PS = 2.  We know QR = 2 too, since that's how rectangles work.  In order for our perimeter to be 10, then, we know that PQ and RS both have to be equal to 3.  We can use these lengths to figure out points Q and R, and now we're almost done:

Remember that whenever you have points on a graph, you can just plug them into the equation (which is y = ax2)!  Let's work with R to avoid negative numbers, but note that this would work the same if we chose to use point Q:

y = ax2
3 = a(1)2 (substitute point R in for x and y)
3 = a