Question

Anyone understands how to solve this question?

Answer 1

See below

Explanation:

A product is `0` only if one of the factors is zero.

`2sinx-1=0` only if `sinx = -1/2`.

On `[0,2pi}`, the numbers with sine equal to `-1/2` are `(7pi)/6` and `(11pi)/6`

`cosx = 0` at `pi/2` and at `(3pi)/2`