Question

Please help??Question will be posted in comment.

Answer 1

Find value of n
\[\sum_{i=1}^{n}(-5+7i)=486\]

Answer 2

So, what is the first value of the sequence(n=1?)?

Answer 3

2

Answer 4

@FibonacciChick666

Answer 5

yea, that's right, so how about when n=2?

Answer 6

9 @FibonacciChick666

Answer 7

good, so now if you add those together, what do you get?

Answer 8

11

Answer 9

right, so now we just think for a moment, if we are successively adding them together, what is your guess for what we need -5+7i to equal when the summation will equal 486?

Answer 10

I have no idea

Answer 11

So, we just want to try guessing to get close

Answer 12

12 @FibonacciChick666

Answer 13

ok so let's see if it seems reasonable, if n=12 we get -5+7(12)=which is two more than 7(11) right?

Answer 14

so that's 79, does it seem plausible that the numbers less than 79 in our sequence add up to 486?

Answer 15

use this link it will give you your answer. http://tutorial.math.lamar.edu/Classes/CalcI/SummationNotation.aspx