Find the exact value of the expression using the provided in

Find the exact value of the expression using the provided information. Find cos(s + t) given that cos 5 =- 1/6, with s in quadrantin III, and cos t = - 3/5, with t in quadrant III 3 + 4 squareroot 35/30 3 - 4 squareroot 35/30 3 - 4 squareroot 37/30 - 3 - 4 squareroot 35/30

Solution

Cos s=-1/6

Here adjacent = 1 hypotenuse=6

Opposite=sqrt(6²-1²)= sqrt35

Sin s=opposite/hypotenuse=-sqrt35/6

Cos t=-3/5

Adjacent=3 and hypotenuse=5

Opposite=sqrt(5²-3²) =4

Sin t=-4/5

Cos(s+t) = cos s cos t- sin s sin t

=(-1/6)(-3/5) - (-sqrt35/6)(-4/5)

= (3-4sqrt35)/30

Correct option is B