Tính:
B = 2 . 4 + 4 . 6 + 6 . 8 + ... + 98 . 100
100+98+96+94+...+8+6+4+2
_______________________
100-98+96-94+...+8-6+4-2
\(\frac{100+98+96+94+...+4+2}{100-98+96-94+...+4-2}\)
\(=\frac{\text{[}\left(100-2\right):1+1\text{]}.102:2}{2+2+2+...+2\left(51s\text{ố}2\right)}\)
\(=\frac{5049}{102}=49\frac{1}{2}\)
tính
B=2*4*6+4*6*8+6*8*10+...+94*96*98+96*98*100
2*4+4*6+6*8+...+98*100+100*102
Tính nhanh 2/2·4+2/4·6+2/6·8+.........+2/96·98+2/98·100
Đặt \(A=\frac{2}{2\cdot4}+\frac{2}{4\cdot6}+\frac{2}{6\cdot8}+...+\frac{2}{96\cdot98}+\frac{2}{98\cdot100}\)
\(A=\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+\frac{1}{6}-\frac{1}{8}+...+\frac{1}{98}-\frac{1}{100}\)
\(A=\frac{1}{2}-\frac{1}{100}\)
\(A=\frac{50}{100}-\frac{1}{100}=\frac{49}{100}\)
2/ 2 * 4 + 2/4 * 6 + 2/ 6 * 8 + ....... + 2/ 98 * 100
2/2.4 + 2/4.6 + 2/6.8 + ... + 2/98.100
= 1/2 - 1/4 + 1/4 - 1/6 + 1/6 - 1/8 + ... + 1/98 - 1/100
= 1/2 + (-1/4 + 1/4) + (-1/6 + 1/6) + ... + (-1/98 + 1/98) - 1/100
= 1/2 - 1/100 = 49/100
Ko viết đàu bài nha!
\(\Rightarrow=\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+\frac{1}{6}-\frac{1}{8}+...+\frac{1}{98}-\frac{1}{100}\)
\(\Rightarrow=\frac{1}{2}-\frac{1}{100}\)
\(=\frac{49}{100}\)
2/2.4 + 2/4.6 + 2/6.8 + ..............+ 2/98.100
=2.(1- 1/4 + 1/4 - 1/6 + 1/6 - 1/8+ .........+1/98 - 1/100)
=2.(1-1/100)=2.99/100 = 99/50
A = 1-2+3-4+5-6+.....+97-98+99-100+101
B = 1+2-3-4+5+6-7-8+......+98-99-100+101
B=1+2-(3+4)+5+6-..-100+101
B=(3+11+19+...+195)-(7+15+...+199)+101
B=25.99-25.103+101
B=-100+101=1
Vậy B=1
a=151
B=1 nha
tinh: 1/2*4 +1/4*6+1/6*8...1/96*98+1/98*100=
ta có : đề bài
=1/2*(2/2*4+2/4*6+2/6*8+...+2/96*98+2/98*100)
=1/2*(1/2-1/4+1/4-1/6+1/6-1/8+...+1/96-1/98+1/98-1/100)
=1/2*(1/2-1/100)
=1/2*49/10
=49/200
Bạn bên trên nhầm 49/100 thành 49/10. Kết quả đúng nhưng bạn ko chú ý dòng thứ 2 từ dưới lên
kết quả phép tính : 1/2*4 +1\4*6 + 1/6*8 + ...+ 1 /96 * 98 + 1 / 98 *100
= 1/2 -1/4 + 1/4 - 1/6 + 1/6 + 1/8 + ... + 1/96 - 1/98 + 1/98 - 1/100
= 1/2 - 1/100
= 49/10
kết quả phép tính : 1/2*4 +1\4*6 + 1/6*8 + ...+ 1 /96 * 98 + 1 / 98 *100
T = 2 .4 + 4 .6 + 6 .8 + ... + 98 x 100 + 100 . 102
Tinh T