Question

Find the value of 2cosx+1=0;0 less than x less than 360°

Answer 1

Answer:

120°; 240°

Step-by-step explanation:

Let's first solve for $cosx$: $2cosx=-1 \rightarrow cosx=-\frac12$ At this point it's just a matter of drawing a circle, and mark where the angle is(please excuse my paint skills, but free hand drawing would be even worse). Red line, is $-\frac12$ on the cosines, and both the green and blue lines are valid solutions. The green line is a quarter of a circle, plus 30°, or 120°. The blue one is 3/4 of a circle, minus 30 degrees, or 240°.