Homework Homework 8 Score 0 of 1 pt 25 of 50 41 complete X 5

Homework: Homework 8 Score: 0 of 1 pt 25 of 50 (41 complete) X 5.3.51 Use the cosine of a sum and cosine of a difference identities to find cos (s+t) and cos (s -t). 5 4 sin s = 13 and sin t=-5, s in quadrant l and t in quadrant lll cos (s + t) = (Simplify your answer, including any radicals. Use integers or fractions for any numbers in the expre las

Solution

sin s = 5/13

sin t = -4/5

cos s = 12/13

cos t = - 3/5

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

plugging the values we get

cos ( s + t) = 12/13 * -3/5 - 5/13 * -4/5

= -36/ 65 + 20 / 65

cos ( s + t ) = -16/65