Question

Which of the following is a solution to 2cos2x − cos x − 1 = 0?\

A. 0 degrees
B. 150 degrees
C. 180 degrees
D. 210 degrees

Answer 1

Option A is correct.

Solution for the given equation is,

Explanation:

Given that : Let then our equation become; .....[1]

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:or and

Simplify:y = 1 and

Substitute y = cos x we have;⇒and⇒

The solution set:

Therefore, the solution for the given equation is, 0 degrees