It would be A. You can find this out by using SOH CAH TOA,
SOH means sin= opposite/hypotenuse
CAH mean cos= adjacent/hypotenuse
TOA means tangent= opposite/adjacent
You would use CAH since you are trying to find cos∠C
You would have cos∠C=10/26.
26 is the hypotenuse since it is opposite the right angle and is the biggest side.
10 is the adjacent since it is right next to C
You would simplify this down to 5/13 by dividing by 2.
This gives you A.
Answer with explanation:
Let us assume that the 2 functions are:
1) f(x)
2) g(x)
Now by definition of concave function we have the first derivative of the function should be strictly decreasing thus for the above 2 function we conclude that

Now the sum of the 2 functions is shown below

Diffrentiating both sides with respect to 'x' we get

Since each term in the right of the above equation is negative thus we conclude that their sum is also negative thus

Thus the sum of the 2 functions is also a concave function.
Part 2)
The product of the 2 functions is shown below

Diffrentiating both sides with respect to 'x' we get

Now we can see the sign of the terms on the right hand side depend on the signs of the function's themselves hence we remain inconclusive about the sign of the product as a whole. Thus the product can be concave or convex.
Given :
Nathan smiled at 50 people one day and recorded that 36 people smiled back at him.
To Find :
How many people should Nathan expect to return a smile if he smiles at 650 people over a period of time.
Solution :
Ratio of people smiled by total number of people is :

Now, it is given that we have to use the given conditions.
Therefore, ratio will be same :

Therefore, number of smiles Nathan expect to return is 468.
(n - 2)*180
Therefore, (8 - 2)*180
Which equals to 6(180) or 1080
Hope this helps! :)