Calculation: (200 + 198 + 196 +) +2）-（1+3+5+… +199）=______ ．

Calculation: (200 + 198 + 196 +) +2）-（1+3+5+… +199）=______ ．

（200+198+196+… +2）-（1+3+5+… +199), = [(2 + 200) × 100 △ 2] - [= (1 + 199) × 100 △ 2] = [202 × 50] - [200 × 50] = (202-200) × 50, = 100

199-198+197-196+195-194+… +5-4+3-2+1．

199-198+197-196+195-194+… +5-4+3-2+1，=（199-198）+（197-196）+… +（5-4）+（3-2）+1，=1+1+… +1，=100．

How to calculate 198 + 197-196-195 + 194 + 193... - 4-3 + 2 + 1 =?

From the first term, the sum of every four terms = 4
198+197-196-195+.+6+5-4-3+2+1
=4×【（198-6）÷4+1】+2+1
=198-2+2+1
=199

Calculation: 198 + 197-196-195 + 194 + 193-192-191 + 190 + 189 -... - 4-3 + 2 + 1
Talking about ideas

Original form
=198+(197-196-195+194)+(193-192-191+190)+189-...+(5-4-3+2)+1
=198+0+1
=199
Idea: use the characteristic that the sum of four consecutive numbers is 0 to group, and then simple operation

Calculate 198 + 197-196-195 + 194 + 193... - 4-3 + 2 + 1 =?

(198 + 197-196-195) + (194 + 193-192-191). (6 + 5-4-3) + 2 + 1 = 4 + 4 + 4... + 4 + 2 + 1 has 49 4, so the original formula = 49 * 4 + 2 + 1 = 199

Find the law of calculation: 1 + 2 + 3 +... 191 + 192 + 193 +... 3 + 2 + 1

193

Calculate 3 + 5 + 7 + 9 + +The value of 195 + 197 + 199 is ()
A. 9699B. 9999C. 9899D. 9799

∵ are all continuous odd numbers, ∵ have a total of (199 + 1) △ 2-1 = 99 numbers, that is: there are 49 pairs of 202 and 99 + 2 = 101 in the middle, ∵ original formula = 202 × 49 + 101 = 9999

1,-1/3,1/5,-1/7,____ ,____ ,____ The 199th number is

1,-1/3,1/5,-1/7,_ 1/9___ ,__ -1/11__ ,__ 1/13__ The 199th number is 1 / 397

1, - 1 / 3,1 / 5, - 1 / 7, (), () () what is the 199th number? {explain why the 199th number is...}

1,－1/3,1/5,－1/7,【1/9】,【－1/11】,【1/13】,……
The nth number of this group is an = [(- 1) ^ (n-1)] × [1 / (2n-1)]
The 199th is: 1 / 397

Find the rule: 1, - 3 / 1,5 / 1, - 7 / 1, () what is the 199th number? {explain why the 199th number is...}

1, - 3 / 1,5 / 1, - 7 / 1. Isn't that 1, - 3,5, - 7
We can see that even terms are negative, so 199 terms are positive,
a1＋（n－1）d＝an
1＋（199－1）＊2＝397
That's 397 / 1