The answer to that is 20x^4
Answer: 2
-7 - (-9) could be visualized as -7 + 9
-7 + 9 is 2
I think this is the answer. if not sorry
Answer:

Step-by-step explanation:
Given: 
To write: the given expression using summation notation
Solution:
Summation notation helps to write a long sum as a single expression.
In the summation notation, the variable
is called the index of summation.
Let
denote a set of n numbers.
Then in summation notation,

