因此我们必须求出三角形的面积。

So, we have to find the area of the triangle.

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这就是空间三角形的面积公式。

That's the formula we've seen for the area of a triangle in space.

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看看三角形的面积。

So, let's look at the area of the triangle.

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谁知道如何计算三角形的面积，请举手。

Who knows how to calculate the area of a triangle, please raise your hand.

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计算下面各三角形的面积。

Work out the area of the following triangle.

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以下哪个三角形的面积与R的面积相等？

Which triangle has the same area as triangle r?

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然后你可以看到在这三角形楔形物里的面积。

Then, you can look at the amount of area inside this triangular wedge.

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下列哪三角形与三角形r的面积相等？

Which of the following has the same area as triangle r.

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下列哪三角形与三角形r的面积相等？

Which of the following has the same area as triangle r.

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