Answer: I believe it is a. Sorry if I am incorrect
Step-by-step explanation:
Functions assign outputs to inputs. The domain of a function is the set of all possible inputs for the function. For example, the domain of f(x)=x² is all real numbers, and the domain of g(x)=1/x is all real numbers except for x=0.
Answer:
b.
Step-by-step explanation:



At

, you have

The trick to finding out the sign of this is to figure out between which multiples of

the value of

lies.
We know that

whenever

, and that

whenever

, where

.
We have

which is to say that

, an interval that is equivalent modulo

to the interval

.
So what we know is that

corresponds to the measure of an angle that lies in the third quadrant, where both cosine and sine are negative.
This means

, so

is decreasing when

.
Now, the second derivative has the value

Both

and

are negative, so we're essentially computing the sum of a negative number and a positive number. Given that

for

, and

for

, we can use a similar argument to establish in which half of the third quadrant the angle

lies. You'll find that the sine term is much larger, so that the second derivative is positive, which means

is concave up when

.