00:02
Okay, so we are now told that we have a function, f -fx, equal to 4x, which is just our linear function with a slope of 4.
00:18
So i don't have a stylus yet, so that's a pretty bad line.
00:23
But imagine that was a straight line with a slope of 4.
00:25
That's what we're dealing with.
00:27
And we are told also that the area under this curve from, one to some unknown value b, let's call that b, is equal to 240.
00:45
And so we're trying to figure out what is this value b? how far from one do we have to go to the right before the area under the line becomes 240? so we use calculus.
00:59
We know that the area under the curve is equal to the definite integral.
01:03
So we've got the definite integral from 1 to b of our function 4x, dx, which is equal to the antiderivative of 4x, which is 4x squared over 2.
01:22
And so this definite integral is equal to this antiderivative evaluated at 1 and at b, and the difference between those two terms.
01:31
So if we expand that, we're going to get 4b squared minus 2, sorry, over 2, minus 4 times 1 squared over 2...