Put spaces when you right the question please, i can't help when all i see is the questions words mashed up together.
The sum of all angles in a triangle has to be 180 so
180-90-73=17
The other non right angle is 17
The sign in the exponent: positive->increases, negative->decreases. Think that a negative sign implies 1/exponential and you'll clearly see the reason.
Answer:
Choice C

Step-by-step explanation:
The quadrant in which an angle lies determines the signs of the trigonometric functions sin, cos and tan
If an angle Θ lies in quadrant IV, cos(Θ) is positive and both sin(Θ) and tan(Θ) are negative
Two of the trigonometric identities we can use are
1.
and
2. 
Using identity 1, we can solve for cos(s) and cos(t)


Since both angles lie in quadrant IV, both cos(s) and cos(t) must be positive so we only consider the positive signs of both values
Using identity 2, we can solve for cos(s-t)

Multiplying numerator and denominator of the first term by
gives us the final expression as
