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# Find the area of the parallelogram with vertices $A (-3, 0), B (-1, 3), C (5, 2)$, and $D (3, -1)$.

## 20 units squared.

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Let's try a parallelogram problem where we're trying to find the area of a parallelogram defined by point A. At -30. We'll call this one a B is negative 1 3 or happy See is that 5 to? We'll call that C. & D. is at three negative one. We'll call that D. In order to find the area of this parallelogram, we need to find vectors A. B. And A D. For example, that we can use to find the area of the entire parallelogram. So A. B. That's just going to be b minus A. Or negative one minus negative three. That'll be two, three minus zero. That'll be three. And since we'll be using the cross product here, the 3rd coordinate is just zero. Similarly, we can find the vector A. D. Which is just d minus a three minus negative three. His six -1 0 is -1. And once again our last coordinate will be zero. Since we're trying to find the cross product A cross B. Let's go ahead and put these vectors and our matrix here. And then we can use the technique from the textbook in order to find this cross product specifically, we can ignore the first coordinate And then look at three times 0 zero times negative one. That's just going to be 0 0. I when we ignore the second column, two times 0 zero times 6 began going to be zero. Rain is zero jay. And lastly, when we ignore the third column two times negative, one -3 times six -3 times six. Okay, writing this all out as one vector That gives us zero I minus zero J, two times negative one is negative two minus 18. That's minus 20. Okay, now the the area of a parallelogram is going to be the magnitude of the vector A crossed B that we just calculated. And since we have no components in the X direction, no components in the Y direction magnitude is just going to be the absolute value of negative 20 which is Just 20 units squared. Thanks for watching.

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