00:01
So for this question, we have some product that has a demand function of q equals 200 minus 2p squared.
00:08
And we're being asked to find what the elasticity of this product is at $5.
00:12
So now here in red, i have written the formula for elasticity, and this is the exact formula as opposed to the non -exact approximation formula where you have delta q over q over delta p over p.
00:27
The most important thing to remember when we're using this exact formula is that the numerator and denominator is kind of switched here, where you have p over q times the derivatives of q in respect to p is of dq over dp.
00:38
So you just need to remember that those are switched in this, that one has p on top and another has p on the bottom.
00:44
But from here is just pretty easy to calculate.
00:47
So dq over dp is what we should start by finding.
00:52
So all we need to do is take the derivative of that q function we had in respect to p.
00:56
So we'll start with 200.
00:58
Derivative of 200 is 0 because the number, derivatives numbers are always 0.
01:02
And now we need to take the derivative of negative 2p squared.
01:06
By this, we do power rule, so that should just be negative 4p because we bring the 2 to the front and 2 times 2 is 4, and then that 2 in the exponent becomes a 1.
01:18
So this should be our derivative.
01:20
And now we're going to switch to green, we just need to plug all of this in.
01:25
So we have e equals the absolute value of p over q times dq over dp is negative for p.
01:37
So before we move on, we actually need to plug in the p and the q value for this.
01:42
So let's find that q value real quick...