tính kết quả dãy tính:
1/1x2+1/2x3+1/3x4+..............+1/15x16=
A.1/16 B.5/16 C.15/17 D.15/16
Trình bày giúp nha mik chả hiểu cái này tí nào ^^
so sánh A và , biết:
A= 10^15+1/10^16+1
B= 10^16+1/10^17+1
tính M :
M = 1x2+2x3+3x4+...+19x20
Tính Nhanh:
a) 3/5+3/16+13/16
b) 1/1x2 + 1/2x3 +1/3x4
a ) 3/5 + 3/16 + 13/16
= 3/5 + ( 3/16 + 13/16 )
= 3/5 + 16/16
= 3/5 + 1
= 3/5 + 5/5
= 8/5
b ) 1/1 x 2 + 1/ 2 x 3 + 1/ 3 x 4
= 1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4
= 1 - 1/4
= 4/4 - 1/4
= 3/4
a) 3/5+3/16+13/16
=3/5+16/16
=3/5+1
=3/5+5/5
=8/5
a =3/5+(3/16+13/16)=3/5+16/16=3/5+1=8/5
b =1-1/2+1/2-1/3+1/3-1/4=1-1/4=3/4
(ở đầu câu mình để dấu bằng để trước dấu bằng bạn viết lại đề bài na)
1/1x2 + 1/2x3 + 1/3x4 +.........................+ 1/15x16
\(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+....+\frac{1}{15.16}\)
\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+.....+\frac{1}{15}-\frac{1}{16}\)
\(=1-\frac{1}{16}\)
\(=\frac{15}{16}\)
Tính hợp lí nếu có thể:
a)3/7+4/9+4/7+5/9
b)1/5+4/10+9/15+16/20+25/25+36/30+49/35+64/40+81/45
c)1/8+1/12+3/8+5/12
d)(1-1/2)x(1-1/3)x(1-1/4)x...x(1-100)
e)9/5:17/15+8/5:17/15
f)2/1x2+2/2x3+2/3x4+...+2/19x20
Ai nhanh nhất mình tick cho
a) 3/7 + 4/9 + 4/7 + 5/9
= ( 3/7 + 4/7 ) + ( 4/9 + 5/9 )
= 7/7 + 9/9
= 1 + 1
= 2
b)1/5 + 4/10 + 9/15 + 16/20 + 25/25 + 36/30 + 49/35 + 64/40 + 81/45
= 1/5 + 2/5 + 3/5 + 4/5 + 5/5 + 6/5 + 7/5 + 8/5 + 9/5
= ( 1/5 + 9/5 ) + ( 2/5 + 8/5 ) + (7/5 + 3/5 ) + ( 4/5 + 6/5 ) + 5/5
= 2 + 2 + 2 + 2 + 1
= 2 x 4 + 1
= 8 +1
= 9
c) 1/8 + 1/12 + 3/8 + 5/12
= ( 1/8 + 3/8 ) + ( 1/12 + 5/12)
= 4/8 + 6/12
= 1/2 + 1/2
= 2/4 = 1/2
mỏi tay rồi
Tìm X:
1:1x2+1:2x3+1:3x4+....+1: (X-1)x X=15:16
Chú ý : dấu chia là phân số
\(\dfrac{1}{1\times2}+\dfrac{1}{2\times3}+\dfrac{1}{3\times4}+...+\dfrac{1}{\left(x-1\right)\times x}=\dfrac{15}{16}\)
\(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+...+\dfrac{1}{x-1}-\dfrac{1}{x}=\dfrac{15}{16}\)
\(1-\dfrac{1}{x}=\dfrac{15}{16}\)
\(\dfrac{1}{x}=1-\dfrac{15}{16}=\dfrac{16}{16}-\dfrac{15}{16}\)
\(\dfrac{1}{x}=\dfrac{1}{16}\)
\(\Rightarrow x=16\)
Cho A = 1/1x2 +1/3x4 + 1/5x6 + ...+1/15x16 + 1/17x18
Chứng tỏ:A=1/10+1/11+1/12+...+1/17+1/18.
Bạn nào giải giúp mình nhé!Nhớ ghi ra cách trình bày (nếu được)
Tks
[ 1/3 + 1/5 ] + [ 1/6 - 1/5 ]
3/16 x 7/5 + 3/5 x 9/16
1/1x2 + 1/2x3 + 1/ 3x4 + ...... + 1/2020x2021
1/1x3 + 1/3x5 + 1/5x7 + ..... + 1/2021 x 2023
3/2 x 1/7 x 5/4 + 15/2 x 6/7 x 1/4
NHỜCÁC BN LM GIÚP MIK GẤP CHIỀU NAY MIK CẦN ÒI !!!!!~~~
TÍNH BẰNG CÁCH NHANH NHẤT NHA CÁC BN
a) \(\left(\frac{1}{3}+\frac{1}{5}\right)+\left(\frac{1}{6}-\frac{1}{5}\right)=\left(\frac{1}{3}+\frac{1}{6}\right)+\left(\frac{1}{5}-\frac{1}{5}\right)=\frac{1}{2}\)
b) \(\frac{3}{16}\times\frac{7}{5}+\frac{3}{5}\times\frac{9}{16}=\frac{21}{80}+\frac{27}{80}=\frac{48}{80}=\frac{3}{5}\)
c) \(\frac{1}{1\times2}+\frac{1}{2\times3}+...+\frac{1}{2020\times2021}=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{2020}-\frac{1}{2021}\)
\(=1-\frac{1}{2021}=\frac{2020}{2021}\)
d) \(\frac{1}{1\times3}+\frac{1}{3\times5}+...+\frac{1}{2021\times2023}=\frac{1}{2}\times\left(\frac{2}{1\times3}+\frac{2}{3\times5}+...+\frac{2}{2021\times2023}\right)\)
\(=\frac{1}{2}\times\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+...+\frac{1}{2021}-\frac{1}{2023}\right)\)
\(=\frac{1}{2}\times\left(1-\frac{1}{2023}\right)=\frac{1}{2}\times\frac{2022}{2023}=\frac{1011}{2023}\)
e) \(\frac{3}{2}\times\frac{1}{7}\times\frac{5}{4}+\frac{15}{2}\times\frac{6}{7}\times\frac{1}{4}==\frac{15}{56}+\frac{80}{56}=\frac{95}{56}\)
Tính nhanh
A=1/2+1/4+1/8+1/16+1/32+1/64+1/128
B=1/1x2+1/2x3+1/3x4+............1/99x100
A=1-1/2+1/2-1/3+1/3-1/4+...+1/64-1/128
A=1-1/128
A=127/128
Vậy A=\(\frac{127}{128}\)
B=1-1/2+1/2-1/3+1/3-1/4+...+1/99-1/100
B=1-1/100
B=99/100
Vậy B=\(\frac{99}{100}\)
Ghi kết quả của phép tính sau: 1/1x2 = 1/2x3 + 1/3x4 + ... + 1/49x50
khó quá sai thì thôi nha
= 1/1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + .... + 1/49 - 1/50
= 1/1 - 1/50
= 49/50
1/1.2 + 1/2.3 + 1/3.4 +.....+ 1/49.50
= 1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 +......+ 1/49 - 1/50
= 1 - 1/50
= 49/50
1/1.2 + 1/2.3 + 1/3.4 +.....+ 1/49.50 = 1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 +......+ 1/49 - 1/50 = 1 - 1/50 = 49/50