Video: Finding Cosine Values of Quadrantal Angles

Find the value of cos 0.

01:22

Video Transcript

Find the value of cos of zero.

Let’s consider a unit circle. On the unit circle, the point one, zero represents zero degrees and zero radians. We’re looking for cos of zero. And it does not have the degree symbol. So we can assume that it’s zero radians.

Cos of angle 𝜃 is equal to the ratio of the adjacent side length over the hypotenuse. Imagine a right triangle like this. Cos of angle 𝜃 would be the ratio of the pink side to the yellow side. The adjacent side length over the hypotenuse.

Here’s another triangle where we have the hypotenuse as yellow and the adjacent side length as pink. When it comes to the unit circle and it comes to cos of zero, the adjacent side and the hypotenuse are of equal length, which means that the cos of zero is equal to one, the adjacent side equal to the hypotenuse at zero.

In fact cos of zero equal to one is an important form that we usually memorise.

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