Question

What is the value of cot840°

Answer 1

cot840=cot(180×5-60)=cot(-60)since cot is negative in second quadrant

cot(-60)=1/(tan(-30))=1/(-1/√3)=-√3

Answer 2

cot 840° =
`√(3)`

Explanation:

First, we must bring the value of 840° down to a value less than 90°.

To do that, we have to consider how many full rotations 840° is on the coordinate plane.

Start by dividing by 360°, since that is one full rotation.

840°/360°=2 R.120

So now we know that 840° is 120° extra, and therefore, the two calues will be equal.

So, cot840°, will be the same as cot120°

But now we need to make 120° a value less than 90°. So we can divide by 90°

120°/90°, and you get 1 R.30°

So now we also know that cot120° = cot 30°

Using your trigonometric table, we see that cot 30° =
`√(3)`

Hope this helped