Question

Select the correct answer. Which of the following is a solution to 2cos2x − cos x − 1 = 0? A. 0° B. 150° C. 180° D. 210°

Answer 1

Option A is correct.

Solution for the given equation is,

Explanation:

Given that :

Let

then our equation become;

A quadratic equation is of the form:

.....[2] where a, b and c are coefficient and the solution is given by;

Comparing equation [1] and [2] we get;

a = 2 b = -1 and c =-1

then;

Simplify:

Simplify:

y = 1 and

Substitute y = cos x we have;

⇒

and

⇒

The solution set:

Therefore, the solution for the given equation is,

Answer 2

A. 0°

Explanation: