Find the value of 1-2+3-4+5-6+...-1000000.

Question

anonymous · Answer

Sum of odd numbers 1,3,....., 999999
- Sum of even numbers 2,4,6,.....,1000000
Use formula from Arithmetic series

anonymous · Answer

SUM OF ODD NUMBERS: 
If N = number of odd terms then sum = (N)^2

SUM OF EVEN NUMBERS: 
Formula: N(N+1) 
How to Find N = (First Even + Last Even)/2 - 1

anonymous · Answer

I know the answer.

angela210793 · Answer

u know how to solve it?"

anonymous · Answer

yes. Just wanted to see how people would tackle it, so that I give a few medals to people.

angela210793 · Answer

ohhhhh :)

anonymous · Answer

Another way of doing this is to notice that

1-2 = -1, 1-2+3 = 2, 1-2+3-4 = -2, 1-2+3-4+5 = 3, 1-2+3-4+5-6 = -3, etc.

So continuing until -1000000, answer should be -100000/2 = -500000.

anonymous · Answer

$$\sum_{n=1}^{1000000}\left( n \right)\left( -1 \right)^{(n+1)}$$
you can also write the summation in terms of the series expansion above!

angela210793 · Answer

tht's wht i was thinking Xactxx