Posted by sh on Thursday, December 9, 2010 at 12:24am.
I need help to start this problem please,
A company can sell 4500 pairs of sunglases monthly when the price is $5. When the price of a pair of sunglasses is increased by 10%, the demand drops to 4250 pairs a month. Assume that the demand equation is linear.
Find the demand equation

Calculus  MathMate, Thursday, December 9, 2010 at 8:05am
Assume the demand equation is linear.
We have two known points:
P1(5,4500), and P2(5.50,4250)
To fit a straight line between two known points, we can apply the twopoint form of line, namely,
(xx1)/(x2x1)=(yy1)/(y2y1)
The equation seems long, but its symmetry makes it very easy to memorize.
Substitute x1=5,y1=4500,x2=5.5,y2=4250, we get
(x5)/(5.505)=(y4500)/(42504500)
250(x5)=0.5(y4500)
y=500x+7000