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Introduction to the trigonometric angle addition identities
Learn about the trigonometric angle addition identities, which help us discuss the trig values of sums of angles in terms of the trig values of the individual angles. For example, we can express sin(x+y) in terms of sin(x), sin(y), cos(x), and cos(y).
Sal reviews all the different trigonometric angle addition identities: sin(a+b), sin(a-c), cos(a+b), cos(a-b), cos(2a), and sin(2a).
Sal evaluates the cosine of the sum of 60° and another angle whose right triangle is given. To do this, he must use the cosine angle addition formula.
Sal evaluates the cosine of twice an angle whose right triangle is given. To do this, he must use the cosine double-angle formula.
Find the trig values of sums of angles whose individual trig values are known.
Sal proves the identity sin(x+y) = sin(x)*cos(y) + cos(x)*sin(y).
Sal proves the identity cos(x+y) = cos(x)*cos(y) - sin(x)*sin(y).