B ( i think )
i might be wrong though
Answer:



Step-by-step explanation:



2nd


3th


What we use?
We use that

and

Answer:
The shaded area is 
Step-by-step explanation:
we know that
The shaded area is equal to the area of the large square minus the area of the two smaller squares
so

Calculate the shaded area
Remember that

substitute

Answer:
a=-3
Step-by-step explanation:
Add the 2 from the left to the right, swapping the sign go be positive over the equal sign.
You then have a+3=0
Subtract the three from both sides:
a=-3
Permutation of 50 is 50! or 50*49*48*47*46.... and so on. I doubt they actually want you to find out what 50*49*48... is, so I'd just put 50!