Question

Find the value of: -1^{2}+2^{2}-3^{2}+4^{2}-5^{2}+6^{2}+....-19^{2}+20^{2}

a.210
b.420
c.630
d.720

Answer 1

@Cammyc

Answer 2

\(-1^{2}+2^{2}-3^{2}+4^{2}-5^{2}+6^{2}+....-19^{2}+20^{2}\)?

Answer 3

Okay so first you might wanna do P.E.M.D.A.S.

Answer 4

Exponents First

Answer 5

yeah

Answer 6

so after you do all the exponents you would get
1+4-9+16-25+36+361+400

Answer 7

after exponents there is mult. but there is none so then you got to add the additions and subtract the subtractions

Answer 8

so its closest to B

Answer 9

Okay so first you might wanna do P.E.M.D.A.S.
you know what pemdas stands for ?

Answer 10

\[-(1^{2}-3^{2}-5^{2}-.....-19^{2})+(2^{2}+4^{2}+...+20^{2})\]

Answer 11

Wait..

Answer 12

yups parenthesis exponents......

Answer 13

"Parentheses, Exponents, Multiplication and Division, and Addition and Subtraction".
YEAH LOL OKAY THEN YOU JUST DO THOSE IN ORDER

Answer 14

If you are taking - common, then in brackets, + will come everywhere..

Answer 15

You can arrange your series as:

\[(2^2 + 4^2 + ... + 20^2) - (1^2 + 3^2 + ... + 19^2)\]

Answer 16

iz der ne other way coz ill juz gt a minute nd a half to solve d ques

Answer 17

You can remember the formula then.. :P

Answer 18

lol

Answer 19

:)

Answer 20

Yes, there is one other way, if you want to follow that, that will be real easy.. :)

Answer 21

yups cn u pls xplain wats dat

Answer 22

Yeah sure..

Do you have calculator. just use that, It will take hardly one minute to calculate overall answer.. :P

Answer 23

lol.....cnt use cal...in gmat

Answer 24

Then, you must do as you don't want to do.. :P

Answer 25

lol

Answer 26

May I give you the formula, may be you are comfortable with that?

Answer 27

yes pls

Answer 28

Here it goes:

\[1^2 + 3^2 + 5^2 + ... upto \; \; + (2n-1)^2 = \frac{n(2n + 1)(2n-1)}{3}\]

Answer 29

May be it is looking dangerous to you, but yes it is..!!

Answer 30

As your last term is 19 so:

\(2n - 1 = 19\)
\(n = 10\)

Answer 31

Just put n = 10 there and find out the sum for square of consecutive odd numbers. :)

Answer 32

alryti understud dis iz mch easier.......thnxx alot mate

Answer 33

Can you find it for even terms or need help??

Answer 34

wud do it....thnx.....

Answer 35

Good..:)