Question

For positive acute angles A and B it is known that tan A 15/8 and Cos B 12/37 find the value of Cos (A+b) being in simplest form

Answer 1

Explanation:

Cos(A + B) = Cos(A)*Cos(B) - Sin(A)*Sin(B)

Find The Hypotenuse of A

Tan(A) = Opposite / Adjacent

Tan(A) = 15/8

Opposite = 15

Adjacent = 8

Hypotenuse = c

c^2 = opposite^2 + Adjacent^2

c^2 = 15^2 + 8^2

c^2 = 225 + 64

c^2 = 289

sqrt(c^2) = sqrt(289)

c = 17

Find the opposite of B

Adjacent = 12

Hypotenuse = 37

Opposite = b

adjacent^2 + opposite^2 = hypotenuse^2

12^2 + b^2 = 37^2

144 + b^2 = 1369

b^2 = 1369 - 144

b^2 = 1335

b = 35

Definitions

Sin(A) = Opposite / hypotenuse = 15/17

Sin(B) = opposite / hypotenuse = 35/37

Cos(A) = 8/17

Cos(B) = 12/37

Answer

Cos(A + B) = Cos(A)*Cos(B) - Sin(A)*Sin(B)

Cos(A + B) = 8/17 * 12/37 - 15/17*35/37

Cos(A + B) = 96/629 - 525/629

Cos(A + B) = -429/629