The denominator of the second fraction can be factored as (a-2)(2a-7), then it becomes doable. You cancel the (2a-7) factors, and are left with:

Do note that you have erased the fact that a≠0 and a≠7/2, so you should always mention that.
Explanation:
tan(arctan x) = x
This is because arctan is the reciprocal of tan. You can view this as the same as 5(1/5x) = x. Since they are reciprocals, when they are multiplied by each other, they cancel each other out.
Answer:
It should be 324.
Step-by-step explanation:
This is an arithmetic series, where S5 means the sum of the first 5 numbers in the series. The general formula is:
Sn = (n/2)(a1 + an)
So,
a1 = 1 + 5/2(1) = 3.5
a5 = 1 + 5/2(5) = 1.5
S5 = (5/2)(3.5+1.5)
S5 = 12.5
<em>The answer should be 12.5</em>