You know, cosine is adjacent over hypotenuse.

你们知道 cos是邻边除以斜边。

That's the cosine of 30 degrees.

这是cos30度。

So the factor by which the slice gets squished down in this direction is exactly cosine of theta.

因，切片 在这个方向上被压扁的因素正是 theta 的余弦。

But let me go back to these sines, cosines and logarithms.

但让我们再来说说正弦、余弦和对数函数。

What's the cosine of 30 degrees?

cos30度是多少？

And compute over 10,000 calculations by cosine, square root and lately Analytic Geometry.

还要完成上万笔计算处余弦，平方根，最近还用起了解析几何。

98 times the cosine of 30 degrees newtons.

98乘以 cos 30度牛顿。

And that's why it's cosine of theta.

因 相等。

Because cosine of 0 right now is 1.

因 相等。

So this is equal to cosine of the angle.

cosθ等于邻边/斜边。

And the cosine of 90 degrees is zero.

90 度的余弦为零。

The cosine of zero is 1.

零的余弦是 1。

However, let's use E dA cosine theta instead of the dot product.

但是，让我们使用 E dA 余弦西塔来代替点积。

As the value t increases, the inside of this cosine function increases more slowly.

随着 t 值的增加，该余弦函数的内部增加得更慢。

To calculate a triangle's shading, we take the  cosine of the angle or theta between the two directions.

为了计算三角形的阴影，我们取个方向之间的角度或 θ 的余弦。

How is knowing cosines gonna help you with your backstroke?

学会余弦对仰泳有什么帮助？

So, the cosine of theta is equal to the (ball’s position) divided by its (amplitude).

因， theta 的余弦等于（球的位置）除以它的（振幅）。

I don't have the slightest idea what sine and cosine mean.

我根本不知道正弦和余弦是什么意思。

It's all just trigonometry, connecting sides and angles through sines and cosines.

这是三角学，上边 以及跨正弦和余弦的角度。

So, the law of cosines is an extension of the pythagorean theorem to the arbitrary angles...

所以余弦定律是勾股定对任意角度的延伸。