Question

Write the sum using summation notation, assuming the suggested pattern continues. -9 - 4 + 1 + 6 + ... + 66

Answer 1

Answer:

Step-by-step explanation:

Answer 2

Answer:

Summation notation is:

$\sum_{n=1}^{16}[5(x-1)-9]$

If you prefer it a little more simplified:

$\sum_{n=1}^{16}(5x-14)$

Step-by-step explanation:

First my favorite part, finding a pattern between the consecutive terms.

This is an arithmetic series because the terms are going up by 5 each time.

So arithmetic sequence, think linear equations:

x     |      y

1            -9

2           -4

3             1

4             6

..................

n             66

We are going to have to find that n but will will eventually...

The equation for a line in point slope form is $y-y_1=m(x_x_1)$ where $(x_1,y_1)$ is a point on the line and m is the slope.

We are already have the slope is 5 (the slope is the common difference in arithmetic sequence).

I'm going to use the first point (1,-9).

So the equation in point slope form is $y-(-9)=5(x-1)$

Subtract 9 on both sides:

$y=5(x-1)-9$

Now we need to know how many terms we are adding so what is x if y=66.

$66=5(x-1)-9$

Add 9 on both sides:

$75=5(x-1)$

Divide both sides by 5:

$15=x-1$

Add 1 on both sides:

$16=x$

We have 16 terms in this sequence where the 16th term is 66.

Summation notation is:

$\sum_{n=1}^{16}[5(x-1)-9]$

You could simplify the 5(x-1)-9.

Distribute:  5x-5-9

Add like terms:  5x-14