Cac bạn giải giúp mình bài toán này với.
Tính theo cách phù hợp nhât
1/2x3 +1/3x4 +1/4x5 +1/5x6 + 1/6x7 +1/7x8 + 1/8x9
giúp mình giải câu này với!!
A = 1 /2x3 + 1/3x4 + 1/4x5 + 1/5x6 + 1/7x8 + 1/8x9
= 1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/7-1/8+1/8-1/9
=1/2-1/9
= 7/18
1/2x3 + 1/3x4 + 1/4x5 +1/5x6 +1/6x7+1/7x8 + 1/8x9
Đặt \(A=\frac{1}{2x3}+\frac{1}{3x4}+\frac{1}{4x5}+\frac{1}{5x6}+\frac{1}{6x7}+\frac{1}{7x8}+\frac{1}{8x9}\)
\(A=\frac{3-2}{2x3}+\frac{4-3}{3x4}+\frac{5-4}{4x5}+\frac{6-5}{5x6}+\frac{7-6}{6x7}+\frac{8-7}{7x8}+\frac{9-8}{8x9}\)
\(A=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}\)
\(A=\frac{1}{2}-\frac{1}{9}=\frac{9}{18}-\frac{2}{18}=\frac{7}{18}\)
1/2x3 + 1/3x4 + 1/4x5 +1/5x6 +1/6x7+1/7x8 + 1/8x9 = 7/18
tinh 1/2x3+1/3x4+1/4x5+1/5x6+1/6x7+1/7x8+1/8x9+1/9x10=
Tra loi:
1/2x3+1/3x4+1/4x5+1/5x6+1/6x7+1/7x8+1/8x9
=1/2 - 1/3 + 1/3 - 1/4 +1/4 - 1/5 + 1/5 -1/6 +1/6 - 1/7 +1/7 -1/8+1/8 - 1/9
=1/2-(1/3-1/3)-(1/4-1/4)-(1/5-1/5)-(1/6-1/6)-(1/7-1/7)-(1/8-1/8)-1/9
=1/2-0-0-0-0-0-0-1/9
=1/2-1/9
=7/18
k cho minh nha!
thông điệp nhỏ
hai tích nếu như ko muốn k
ai tích mình tích lại
Tính nhanh
1/1x2 + 1/2x3 + 1/3x4 + 1/4x5 + 1/5x6 + 1/6x7 + 1/7x8 + 1/8x9 + 1/9x10
Mình ko có biết viết phân số. Mọi người giúp mình nha, mình đang cần gấp lắm
1/1x2+1/2x3+1/3x4+..+1/9x10
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5+...-1/10
=1-1/10
=9/10
Tính nhanh B =(1/2x3 + 1/3x4 + 1/4x5 +1/5x6 +1/6x7+1/7x8 + 1/8x9 + .... + 1/50x51) + ( 5/6 + 19/ 20 + 41/42 + 71/72 + .... + 2549/2550 )
\(B=\left(\dfrac{1}{2\cdot3}+\dfrac{1}{3\cdot4}+...+\dfrac{1}{50\cdot51}\right)+\left(\dfrac{5}{6}+\dfrac{19}{20}+...+\dfrac{2549}{2550}\right)\)
\(B=\left(\dfrac{1}{2\cdot3}+\dfrac{1}{3\cdot4}+..+\dfrac{1}{50\cdot51}\right)+\left(1-\dfrac{1}{2\cdot3}\right)+\left(1-\dfrac{1}{3\cdot4}\right)+...+\left(1-\dfrac{1}{50\cdot51}\right)\)
\(B=\left(1+1+...+1\right)+\left(\dfrac{1}{2\cdot3}+\dfrac{1}{3\cdot4}+...+\dfrac{1}{50\cdot51}\right)-\left(\dfrac{1}{2\cdot3}+\dfrac{1}{3\cdot4}+...+\dfrac{1}{50\cdot51}\right)\)
\(B=1\cdot49=49\) (vì có (50 - 2) : 1 + 1 = 49 số hạng 1)
2/2x3+2/3x4+2/4x5+2/5x6+2/6x7+2/7x8+2/8x9+2/9x10
các bạn giúp mình với nhé
Bài làm:
\(\frac{2}{2.3}+\frac{2}{3.4}+\frac{2}{4.5}+...+\frac{2}{9.10}\)
\(=2\left(\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{9.10}\right)\)
\(=2\left(\frac{3-2}{2.3}+\frac{4-3}{3.4}+\frac{5-4}{4.5}+...+\frac{10-9}{9.10}\right)\)
\(=2\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{9}-\frac{1}{10}\right)\)
\(=2\left(\frac{1}{2}-\frac{1}{10}\right)=2.\frac{4}{10}=\frac{4}{5}\)
a)1,27+2,77+4,27+5,77+...+31,27+32,77
b)1/1x2+1/2x3+1/3x4+1/4x5+1/5x6+1/6x7+1/7x8 +1/8x9+1/9x10
mình cần gấp
\(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+.....+\frac{1}{9.10}\)
\(=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{9}-\frac{1}{10}\)
\(=1-\frac{1}{10}\)
\(=\frac{9}{10}\)
chúc bn học tốt
\(1,27+2,77+4,27+5,77+...+31,27+32,47\)
\(=\left(1,27+32,77\right)+\left(2,77+31,27\right)+....+\left(16,27+17,77\right)\)
\(=34,04+34,04+....+34,04\)( 11 số hạng)
\(=34,04.11=374,44\)
chúc bn học tốt
b)\(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{9.10}\)
\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{9}-\frac{1}{10}\)
\(=1-\frac{1}{10}\)
\(=\frac{10}{10}-\frac{1}{10}\)
\(=\frac{9}{10}\)
Tính 1/3x4+1/4x5+1/5x6+1/6x7+1/7x8+1/8x9+1/9x10+1/10x11+1/11x12
= 1/3 - 1/4 + 1/4 - 1/5 + 1/5 - 1/6 + 1/6 - 1/7 + 1/7 - 1/8 + 1/8 - 1/9 + 1/9 - 1/10 + 1/10 - 1/11 + 1/11 - 1/12
= 1/3 - 1/12 = 1/4
tính nhanh
1x2 + 2x3 + 3x4 + 4x5 +5x6 + 6x7 + 7x8 + 8x9 + 9x10