Find all solutions to the equation. cos x = -1/2

 ^^

Step-by-step explanation:

You didn't add the range. I'll use (0<x<2π)

cosx = -1/2

x=-cos-¹(1/2)

x= -60°

Cosine is negative in the second and 3rd quadrants

180-x Second quadrant

x+180 3rd quadrant

So

Our answer

180-(-60)=240° or 4π/3 second quad

180+(-60) = 120° or 2π/3 3rd quad

we have three similar triangles, because each has a right angle and shares an angle.   let's write the angles in order: opposite to short leg, long leg, hypotenuse.

cab similar to bad similar to cbd

or as ratios,

ca: ab: cb = ba: ad: bd = cb: bd: cd

we also know

ac = ad + cd

(ad+cd): ab: cb = ba: ad: bd = cb: bd: cd

(ad+cd)/cb=cb/cd

we have cb=6, ad=5 and seek x=cd.

we reject the negative root and conclude x=4

answer: 4