Shu Ren Education and Training Center, Jiangsu Province, Grade 6 Mathematics 20 1/summer vacation Lecture 7 Comprehensive operation (2) Extracurricular exercises1,2, 3, what should I do?

The second question, (1+100) *100/2 = 5050.

The answer to the third question is 9900.

S99= 1*2+2*3+3*4+4*5+。 . . +99* 100

S98= 1*2+2*3+3*4+4*5+.。 . 98*99

Then s99-s98 = 99 * (100-98) = 99 * 2.

S98-S97=98*(99-97)=98*2

S97-S96=97*(98-96)=97*2

. . .

S2-S 1=2*(3- 1)=2*2

The left and right sides of the above formula are added separately.

S99-S 1=2*(2+3+4+5。 . . . +98+99)

S99=2*( 1+2+3+4+5+.。 . . 98+99)= 990 Respondents: Enthusiastic users | 201-7-912: 21.

2. Try to find the value of 1+2+3+4++100 = (1+100)+(2+99)+...+(50+5/kloc-0)

***50 is 5050.

3. Order S99 =1x2+2x3+3x4+4x5+...+99x100.

S98= 1x2+2x3+3x4+4x5+......98*99

Then s99-s98 = 99 * (100-98) = 99 * 2.

S98-S97=98*(99-97)=98*2

S97-S96=97*(98-96)=97*2

......

S2-S 1=2*(3- 1)=2*2

The left and right sides of the above formula are added separately.

S99-S 1=2*(2+3+4+5......+98+99)

S99 = 2 * (1+2+3+4+5+... 98+99) = 9900 Respondents: 123asd456wer | Level 1 | 201-7-65446.