
The formula of the sum of the arithmetic sequence:

calculate:

substitute

Your answer is:
Expression simplified: 
Step-by-step explanation:
The expression that we have in this problem is:

The first type of operation that we have to solve in such expression are multiplication/division.
In this expression, there is only one multiplication, that is:

So we can rewrite the expression as

Now we can evaluate the sum of the similar terms: in this case, similar terms are only 3 and 4, and their sum is

Therefore, the expression can be rewritten as

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The complete factorization of the equation 81x² - 100 is; (9x - 10)(9x + 10)
<h3>How to factorize quadratic equations?</h3>
We are given the quadratic equation;
81x² - 100
Now, according to quadratic identities, we know that;
(a + b) * (a - b) = a² - b²
Now, our equation can also be expressed as;
81x² - 100 = 9²x² - 10²
Thus, applying the quadratic identity gives us;
(9x + 10)(9x - 10)
Read more about factorization of quadratic equations at; brainly.com/question/1214333
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