00:01
Okay, we want to do this integral over region r.
00:04
That's this triangle in the xy plane, okay? so i'm gonna do a variable change.
00:15
I have to figure out what it is.
00:18
But so those three lines that define that triangle are these.
00:24
Now, what i'm gonna do is i'm gonna change the variables u and v.
00:29
I'm gonna do a linear transformation that leaves the origin intact, but we'll move these points so that we have a triangle that lies along one of the axes and the other edge of the triangle will be parallel to the other axis.
00:48
The reason for doing that is that this way, i would actually have to do two integrals, for instance, because if i draw my rectangles vertically, i'd have some of them contact the curve y equals 2x above and the other would hit this line down here up above.
01:11
And so rather than do that, i'm gonna write it as one integral.
01:18
So i'm gonna change to u and v like this.
01:24
And so at the point x equals 1, y equals 2, i want u and v both to equal 1.
01:41
And at the point x equals 2, y equals 1, i want u equals 0 and v equals 1.
01:54
And so i can plug those in and i can solve for a and b and c and d...