This is the rule of sums of trig identities. It says that sin(a + b) = sina*cosb+sinb*cosa. Set up your right triangles. In a 30-60-90 triangle, the side across from the 60 angle is the square root of 3, the side across from the 30 is 1, and the hypotenuse is 2. In a 45-45-90 the sides across from the 45 degree angles are 1 and the hypotenuse is square root of 2. With that being said, the sin of 60 is 
and the cos of 60 is 1/2. Both the sin and cos of 45 is 
. So your formula is filled in like this: 
. When you do the multiplication on those sets of parenthesis, you get 
. When you add those your solution is 
. Depending upon your instructor you may have to rationalize that denominator to get that radical out from under there, but if not, that's pretty much it!
If triangle ABC ~ triangle DEC, find AC.
1 answer:
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