Trig Equations #12

There are many different trig equations. An example of a sum and difference equation would be cos105 degrees. You must add two degrees together to make 105. Use the equation cos(x+y)=cosxcosy-sinxsiny. Cos(60+45) equals to 105 degrees, so now, you must find the sine and cosine of 60 and 45 degrees. Then, just plug them into the equation. An example of a double angle would be sinx=-1/4, solve for cos2x and sin2x. First, you would use the identity cos2x=cos^2x - sin^2x. In order to find cosx, use the identity sin^2x + sin^2x = 1. Since sin is already given, plug it in and solve for cos.