# [SOLVED] SAT math page 656

• Sep 28th 2008, 01:46 AM
fabxx
[SOLVED] SAT math page 656
In the figure below, PQRS is a rectangle, and points Q and R lie on the graph of y=ax^2, where a is a constant. If the perimeter of PQRS is 10, what is the value of a?

From the graph I got that the length of the rectangle is 3 and the width is 2. Is this correct? I don't know what to do next. Thanks in advance
• Sep 28th 2008, 02:14 AM
Moo
Quote:

Originally Posted by fabxx
In the figure below, PQRS is a rectangle, and points Q and R lie on the graph of y=ax^2, where a is a constant. If the perimeter of PQRS is 10, what is the value of a?

From the graph I got that the length of the rectangle is 3 and the width is 2. Is this correct? I don't know what to do next. Thanks in advance

You know that the distance PQ is 3.
The coordinates of P are (-1;0). Since PQ is parallel to the y axis, their x-ordinate are the same : -1.
And the distance PQ will be the difference between their y-ordinates.
So point Q has coordinates (-1;3)

Now, substitute them into y=ax˛ to get a.
• Sep 28th 2008, 02:40 AM
fabxx
is it like this?

Because y=3 and x=(-1)
and because y=ax^2
so therefore 3=a(-1)^2
so a=3?

• Sep 28th 2008, 02:42 AM
Moo
Quote:

Originally Posted by fabxx
is it like this?

Because y=3 and x=(-1)
and because y=ax^2
so therefore 3=a(-1)^2
so a=3?