Tính B = 1 + 2 + 3 + ... + 98 + 99 theo 2 cách
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Những câu hỏi liên quan
DT
2
0N
5
9 tháng 9 2016
Tính theo cách thuận tiện nhất:
1 + 2 + 3 + 99 + 98 + 97
= ( 1 + 99 ) + ( 2 + 98 ) + ( 3 + 97 )
= 100 + 100 + 100
= 100 x 3
= 300
NT
2
12 tháng 1 2017
mình chỉ biết câu b thôi
b , 1+2-3-4+5+6-7-8+.......+97+98-99-100+101
=1+(2-3-4+5)+(6-7-8+9)+......+(98-99-100+101)
=1+0+0+.....+0
=1
bạn nè có viết thiếu đề ko rứa nếu mình sửa lại đề thi bài mình làm đúng rồi đó
18 tháng 3 2018
b)1+2-3-4+5+6-7-8+.....+97+98-99-100
=(1+2-3-4)+(5+6-7-8)+...+(97+98-99-100)
=-4+(-4)+...+(-4)
mà biểu thức có 25 nhóm
=>biểu thức=25(-4)=-100
NP
1
CM
15 tháng 1 2019
=(1+98-99-100)+(2-3-4+5)+(6-7-8+9)+...+(95-96-97+98)
=-100+0+0+0+0+0.........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................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31 tháng 1 2022
a: Tính B
Số số hạng là 99-1+1=99(số)
Tổng là:
\(\dfrac{\left(99+1\right)\cdot99}{2}=50\cdot99=4950\)
b: Tính C:
SỐ số hạng là (999-1):2+1=500(số)
Tổng là:
\(\dfrac{\left(999+1\right)\cdot500}{2}=500^2=250000\)
C1 .B=1+2+3+4+...+99
B=[(99-1):1+1]X(99+1):2
B=99x100:2
B=4950
C2
ta có từ 1 -> 99 có 99 số
=> B= 1+2+3+...+98+99
B= (1+99)+(2+98)+...+50
B= 100+100+...+50 ( 49 SỐ 100 , VÌ TỪ 1 -> 99 TẠO THÀNH 49 CẶP VÀ THỪA SỐ 50)
=> B=100X49+50
B= 4950
B = 1 + 2 + 3 + ... + 98 + 99
Cách 1 :
Tổng B có số số hạng là :
( 99 - 1 ) : 1 + 1 = 99 ( số )
Tổng B bằng :
( 1 + 99 ) x 99 : 2 = 4950 .
Cách 2 : B = 1 + 2 + 3 + ... + 98 + 99
= ( 1 + 99 ) + ( 2 + 98 ) + ( 3 + 97 ) + ... + ( 49 + 51 ) + 50
= 100 + 100 + 100 + ... + 100 + 50
Tổng B có số số hạng là :
( 99 -1 ) : 1 + 1 = 99 ( số )
Mà cứ 2 số hạng lại ghép thành 1 tổng , suy ra có :
99 : 2 = 49 ( tổng ) và dư 1 số hạng ( 50 )
Vậy : B = 100 x 49 + 50
B = 4950 .