1/1x5/5
1+1x5:5=...
1 + 1 x 5 : 5
= 1 + 1 x 5 : 5
= 1 + 1 x 1
= 1 + 1
= 2
tinh nhanh (5/12+1/2x1/3):(2x1/3-1x5/12)
\(\left(\frac{5}{12}+\frac{1}{2}.\frac{1}{3}\right):\left(2.\frac{1}{3}-1.\frac{5}{12}\right)\)
\(=\left(\frac{5}{12}+\frac{1}{6}\right):\left(\frac{2}{3}-\frac{5}{12}\right)\)
\(=\frac{7}{12}:\frac{1}{4}\)
\(=\frac{7}{3}\)
_Chúc bạn học tốt_
5/1x5+5/3x5+5/5x7+.....+5/99x101
sửa đề nhé:
\(\frac{5}{1\times3}+\frac{5}{3\times5}+...+\frac{5}{99\times101}\)
\(5\times\frac{1}{2}\times\left(\frac{2}{1\times3}+\frac{2}{3\times5}+...+\frac{2}{99\times101}\right)\)
\(=\frac{5}{2}\times\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+...+\frac{1}{99}-\frac{1}{101}\right)\)
\(=\frac{5}{2}\times\left(1-\frac{1}{101}\right)\)
\(=\frac{5}{2}\times\frac{100}{101}\)
\(=\frac{250}{101}\)
so sánh 2/1x5+3/5x11+4/11x19+5/19x29+6/29x41 và 1/1x4+2/4x10+3/10x19+4/19x31
Đặt \(A=\dfrac{2}{1.5}+\dfrac{3}{5.11}+\dfrac{4}{11.19}+\dfrac{5}{19.29}+\dfrac{6}{29.41}\)
\(2A=\dfrac{4}{1.5}+\dfrac{6}{5.11}+\dfrac{8}{11.19}+\dfrac{10}{19.29}+\dfrac{12}{29.41}\)
\(2A=\dfrac{1}{1}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{11}+\dfrac{1}{11}-\dfrac{1}{19}+\dfrac{1}{19}-\dfrac{1}{29}+\dfrac{1}{29}-\dfrac{1}{41}\)
\(2A=\dfrac{1}{1}-\dfrac{1}{41}=\dfrac{40}{41}\)
\(A=\dfrac{40}{41}:2=\dfrac{20}{41}\)
Đặt \(B=\dfrac{1}{1.4}+\dfrac{2}{4.10}+\dfrac{3}{10.19}+\dfrac{4}{19.31}\)
Tương tự ta dễ dàng tình đc:
\(B=\dfrac{10}{31}=\dfrac{20}{62}\)
Ta có: \(\dfrac{20}{41}< \dfrac{20}{62}\Rightarrow A< B\)
Vậy ........................
Chúc bn học tốt
Đặt A=2/1.5+3/5.11+...+6/29.41
B=1/1.4+2/4.10+3/10.19+4/19.31
2A=4/1.5+6/5.11/+...+12/29.41
2A=1-1/5+1/5-1/11+...+1/29-1/41
2A=1-1/41
2A=40/41
A=20/41
3B=3/1.4+6/4.10+9/10.19+12/19.31
3B=1-1/4+1/4-1/10+1/10-1/19+1/19-1/31
3B=1-1/31
3B=30/31
B=10/31
Vì 10/31<20/41 nên B<A
Giải:
Đặt \(A=\dfrac{2}{1.5}+\dfrac{3}{5.11}+\dfrac{4}{11.19}+\dfrac{5}{19.29}+\dfrac{6}{29.41}\)
\(A=\left(\dfrac{4}{1.5}+\dfrac{6}{5.11}+\dfrac{8}{11.19}+\dfrac{10}{19.29}+\dfrac{12}{29.41}\right):2\)
\(A=\left(\dfrac{1}{1}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{11}+\dfrac{1}{11}-\dfrac{1}{19}+\dfrac{1}{19}-\dfrac{1}{29}+\dfrac{1}{29}-\dfrac{1}{41}\right):2\)
\(A=\left(\dfrac{1}{1}-\dfrac{1}{41}\right):2\)
\(A=\dfrac{40}{41}:2\)
\(A=\dfrac{20}{41}\)
Đặt \(B=\dfrac{1}{1.4}+\dfrac{2}{4.10}+\dfrac{3}{10.19}+\dfrac{4}{19.31}\)
\(B=\left(\dfrac{3}{1.4}+\dfrac{6}{4.10}+\dfrac{9}{10.19}+\dfrac{12}{19.31}\right):3\)
\(B=\left(\dfrac{1}{1}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{10}+\dfrac{1}{10}-\dfrac{1}{19}+\dfrac{1}{19}-\dfrac{1}{31}\right):3\)
\(B=\left(\dfrac{1}{1}-\dfrac{1}{31}\right):3\)
\(B=\dfrac{30}{31}:3\)
\(B=\dfrac{10}{31}\)
Vì \(\dfrac{20}{41}>\dfrac{10}{31}\) nên A>B
1X5+1X5=
=10
các bạn cho mình vài li-ke cho tròn 545 với
1X5+1X5=
cần tìm 1 boy friend ,nhớ kết bạn
1+1X5+5+8:4+9:3=???????/đổi tích nha 3 tiv lun
giải giúp minh với
tìm x
1/1x5 + 1/ 5x9 + 1/ 9 x3 + 1/ 17x21 x X = 2/5
Tính:
(2007 - 2005) + (2003 - 2001) +...+ (7 - 5) + (3 - 1)
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Viết tiếp 3 số hạng thứ 8;9 và 10 của dãy số sau: \(\dfrac{1}{1x5};\dfrac{1}{5x9};\dfrac{1}{9x13};...\)