Prime numbers are those numbers which only are divisable by 1 and itself. 5 is prime, because only 1 and 5 divide into 5 evenly. However, 9 is NOT prime because 3 also divides into 9.

So to prime factor 245, we need to find its prime factors, the prime factors of 245 are 7, 7, 5 we know this because 7*7*5 = 245.

A rule of radicals states that = *
Now simplfy each square root, and can not be simplfied
Mulply the two together and you get

is the same, the prime factors of 80 are (2*2*2*2*5)
Rewrite as
Simply

Now, as for the missing length of right triangles, you must use the pythagorean therom
Plug in what you know
Simplfy
Simplfy
so and use the process from above to simplfy

For the last problem, I am assuming that A = 2 since a length of a triangle leg can not be negative,

The square of any square root is the number so we have