Raw Transcript
Hello, Tom from everystepcalculus.com and everystepphysics.com. Double Integral today. On this video. Um, so let’s do it. Index 8 to get to my menu. We’re going to scroll down to the D section. You can use the second and then the arrow to go, you know, quicker. Screen by screen. But there is Double Integral right there. And we’re going to enter our function and we’re going to press Alpha first before you enter anything into these entry lines, here. Alpha X times Y plus X squared times Y cubed. I always show you what you’ve entered, you can change it if you want. And now we have to decide whether we want to do it from dy, dx or dx, dy, that’s the order of integration. We’re going to go with number 2, dy, dx. And here we have if dx is on the outside then it’s on the outside here and this is on the inside therefore the ay by is, the limits are involved with the dy inside. So remember that. dx is on the outside therefore these go with the dx. dy is on the inside the limits of integration go from ay to by. So let’s enter those now. And there’s the region. Just like this in notation. So we’re going to do Alpha 1 to Alpha 3. Say it’s okay. We’re going to do Alpha 0 to Alpha 2. I say that’ okay. And there’s out integral right there. We have the function inside here, dy dx. And here’s the x on the outside and the limits of integration 0 to 2 on the inside. So with respect to Y, we integrate with respect to Y. Here’s the answer x squared times y to the fourth over 4 plus x times y squared over 2. And we’re going to do that over the 0 on the 2 limits. So at x equals 2, you add. You see quotation marks here but I can’t, I would like to put parentheses in for those because we’re substituting y equals 2 for all the y’s in this function, here. So you’re going to have to put the parentheses in every time you see quotation marks, put parentheses, okay. And then 4 squared plus 2 x and that’s what that equals and then y equals 0 and then here’s the 0’s in for Y and that equals 0. And 4 x squared plus 2x minus. The upper limit minus the lower limit is 4x squared plus 2 times x. Now we integrate that with respect to the limits 1 and 3 with respect to x. So we integrate that. Here’s the answer here. 4x cubed divided by 3 x squared over 1 in 3. The limits. And x equals 3 here, we’re substituting 3 in for all the x’s equals 45. And x equals 1. You substitute 1 for all the x’s, you get 7/3. So upper minus lower 45 minus 7/3 equals the are is 42.7 square units. Remember the an integral always gives\you the area under a curve. And so I always put square units in there. Alright, have a good one.
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