can anyone please help me on a math problem and explain how they got the answer. thanks so much.?

Question

What is the sum of the elements in the following sequence
-1,3,-5,7,-9,11, ...,-441 ?

Answer 1

-1+3-5+7-9+...-441
Regrouping:
(-1+3)+(-5+7)+....(-437+439) - 441.
2+2+2+2+.....+2 - 441.
There are 110 2's, because there are 220 terms besides the last term in the sequence, which is not grouped.

2*110 - 441 = -221.

Answer 2

Here is what I did, and there probably is an easier way:

1. -1 = -1
2. +3 = +2
3. -5 = -3
4. +7 = +4
5. -9 = -5

so i stopped here and noticed a pattern.. notice how the first term = -1, the second term = +2, the third term = -3. So, the pattern is the # of the term = the sum, where the odd term = a negative # and the even terms = positive #'s.

So, we know the sequence stops at 441. To determine how many terms there are we take 441/2 = 220.5 = 221. I checked this by typing 1, 3, 5, 7, 9 in to cells in Excel, and dragging the sequence down -- yes, 221 terms.

Therefore, since we know there are 221 terms, according to our pattern we noticed:

221. -441 = -221.

Answer 3

In the sequence, the odd terms (1st, 3rd, 5th,...) are -ve and the even terms are +ve.

So -441 is an odd term being a -ve number.

Also the n-th term, without considering the sign is (2n - 1)

Put 2n - 1 = 441
n = 221
So -441 is the 221st term.

Now the sum of the 1st and the 2nd terms, the 3rd and the 4th terms, the 5th and the 6th terms,....and so on is always 2.
You have 110 such pairs which add up to 2 x 110 = 220.
The 221st term is -441.

So the sum of the sequence is 220 - 441 = -121.

Hope this helps.

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Answer 4

-1,3,-5,7,-9,11, ...,-441

-1-5-9-13-...-441
+3+7+11+15+19+....
=?

or

(-1+3)+(-5+7)+...
=2+2+2+....
=?
How many 2s?

Answer 5

I put the series into an excel spreadsheet and added up the series. It turns out to be -221. There are 221 terms. It happens to be that the sum of the series is the positive number of terms for an even number of terms or the negative number of terms for an odd number of terms.

Answer 6

x is entire a is women x-a is boys (x-a)/(a-15) = sixteen/9 (a-15)/(x-a-40 5) = 9/7 9(x-a) = sixteen(a-15) 7(a-15) = 9(x-a-40 5) 9x-9a = 16a-240 9x = 25a-240 x = (25a-240)/9 7a-one 0 five = 9x-9a-405 16a+3 hundred = 9[(25a-240)/9] 16a+3 hundred = 25a-240 540 = 9a 60 = a x = [(25(60)-240)/9] x = (1500-240)/9 x = 1260/9 x = one hundred forty one hundred forty scholars.

Answer 7

an=(-1)^n*(2n-1) so
a1=-1;a2=3;a3=-5....
2n-1=441 => 2n=442=>n=221
-1+3-5+7-9+11-.....-441=
(-1-5-...-441)+(3+7+...+339)=
-(1+5+...+441)+(3+7+...+339)=
-[(111/2)(1+441)]+[(110/2)(3+339)]=
-[(111/2)442]+[(110/2)442]=
-24531+24310=
-221

Answer 8

>>>>>minus infinity <<<<<

Answer 9

you have to make an equation. or, you can do it on a calculator manually