Solving Trigonometric Equations III

Solve trig equations using identities, squaring both sides, and using the quadratic formula

[helirivera]

WHY DOES THE RATIO REMIND YOU OF A 30-60-90? HOW DO ANY RATIOS REMIND US OF ANY TYPE OF TRIANGLE?

[themontaukmonster]

hello, what indicates that you must use the inverse (cos^-1) to solve the problem?

[andrearueda]

How does foiling it give u that equation in the second

[amandamariscal]

How would I check the solutions if I don't have a graphing calculator like yours?

[charanjotsingh]

where this equation came from? cos(2x)= cos^2(x)-sin^2(x)

[mahmoudwahidi]

i hate how you literally leave an important lesson like what youve shown at the end to be brought up as an "oh by the way haha! this angle is also!! part of the solution" instead of actually taking the time to explain why that's the case in more depth for the less experienced