00:01
So here we're talking about elasticity.
00:02
We're given a demand curve.
00:04
The quantity x is equal to 600 minus 40p.
00:08
We're told the price is equal to 1, which means x is equal to 600 minus 40 is equal to 560.
00:15
Great.
00:17
The elasticity of demand.
00:18
So we usually call this elasticity squiggly e epsilon, which is equal to the percent change in quantity over the percent change in price.
00:28
Right? that's the definition of elasticity, but that can be written as the raw change relative to the base change.
00:35
That's the formula for percentage change.
00:38
And that can be written in terms of calculus as dx over x, d .p over p.
00:48
And that's dxdp times p over x.
00:53
Now we know from basic calculus that dx, dx, d .p, that's just the slope.
00:58
Right? it's minus 40...