Question

Co(-150degree)=positive or negative cos150degree?please give answer with explanation

Answer 1

See my lengthy validation logic, for `cos ( +- 150^o) = - sqrt 3/2`. ..

Explanation:

Use `0 <= sqrt ( x^2 + y^2 ), ( x, y ) = r ( cos theta , sin theta )`.

`Q_1 rArr x, y >= 0, Q_2 rArr x<= 0, y >= 0, Q_3 rArr x, y <= 0`

`and Q_4 rArr x >= 0, y <= 0`

Anticlocwise `150^o in Q_2` and clockwise #- 150^o in Q_3., and

in both `x<= 0`, and so, `x = r cos theta <=0`

# rArr cos (+- 150^o) <= 0.

So, for both, your calculator displays the same `- 0.866025403..`

that is 9-sd approximation to `- sqrt3/2`.

After reading my answer, I hope that you would invalidate negative

r, in problems.