Which of the following is a solution to 2cos x + 1 = 0? 60° 120° 210° 300°
2 answers:
Answer:
correct answer is second option (The solution of
is
)
Step-by-step explanation:
In this question we have given


therefore,


therefore,

because cos(120)=
Therefore,
The solution of
is 
Rewrite <span>2cos x + 1 = 0 as:
2 cos x = -1, and then cos x = -1/2
x must be in Quadrant II or Quadrant III, since the adj. side is negative.
Note that the angle 120 has adj. side -1 and hyp 2. So 120 degrees is one solution.
Now what about a possible 2nd solution, to be found in Quadrant III? That would be -120 degrees, which has the same terminal line as does 240 degrees.
No soap.
So, the solution is 120 degrees.</span>
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