Tính :
a. 2.3/5 : 2.1/4 + 5/2
b. 16/6 - 2.1/6 : 1.1/7
Những câu hỏi liên quan
3x.(1/1.1/2+1/2.1/3+1/3.1/4+1/4.1/5+1/5.1/6)=3/4
bài 1:tính số hạng có trong các tổng sau:
1.1-2+3-4+5-6+7-8
2.1-3+5-7+9-11+13-15
3.-1+3-5+7-9+11-13+15
4.2-4+6-8+10-12+14-16+18-20
5.-2+4-6+8-10+12-14+16-18+20
6.2-5+8-11+14-17+20-23+26
7.-1+5-9+13-17+21-25+29-33+37
8.1-5+9-....-81+85-89+93
9.2-4+6-8+....+202-204
10.1-6+11-16+21-....+176-181
Tính : a, S = 1+4+7+10+13+......+301 b,S= 1+5+9+13+.....+ .... c, S= 1+2-3-4+5+6-7-8+9+10-11-12+..... +41+42-43-44 d, S= 2.1+2.2+2.3+2.4+....+2.99 mình đang can khan cap nho cac ban lam cho minh ti voi
1.1/3-2√2 + 1/2+√5 2.1/√3+√7 + 2/1-√7 3.a-2√a/2-√a 4.x√y+y√x/√x+√y
1: \(\dfrac{1}{3-2\sqrt{2}}+\dfrac{1}{\sqrt{5}+2}\)
\(=\dfrac{3+2\sqrt{2}}{1}+\dfrac{\sqrt{5}-2}{1}\)
\(=3+2\sqrt{2}+\sqrt{5}-2=2\sqrt{2}+\sqrt{5}+1\)
2: \(\dfrac{1}{\sqrt{3}+\sqrt{7}}+\dfrac{2}{1-\sqrt{7}}\)
\(=\dfrac{\sqrt{7}-\sqrt{3}}{4}+\dfrac{2\left(1+\sqrt{7}\right)}{-6}\)
\(=\dfrac{\sqrt{7}-\sqrt{3}}{4}-\dfrac{1+\sqrt{7}}{3}\)
\(=\dfrac{3\left(\sqrt{7}-\sqrt{3}\right)-4\left(\sqrt{7}+1\right)}{12}=\dfrac{-\sqrt{7}-3\sqrt{3}-4}{12}\)
3:
\(=\dfrac{\sqrt{a}\left(\sqrt{a}-2\right)}{2-\sqrt{a}}=-\dfrac{\sqrt{a}\left(\sqrt{a}-2\right)}{\sqrt{a}-2}=-\sqrt{a}\)
4:
\(=\dfrac{\sqrt{xy}\left(\sqrt{x}+\sqrt{y}\right)}{\sqrt{x}+\sqrt{y}}\)
\(=\sqrt{xy}\)
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1) \(\dfrac{1}{3-2\sqrt{2}}+\dfrac{1}{\sqrt{5}+2}\)
\(=\dfrac{3+2\sqrt{2}}{\left(3-2\sqrt{2}\right)\left(3+2\sqrt{2}\right)}+\dfrac{\sqrt{5}-2}{\left(\sqrt{5}+2\right)\left(\sqrt{5}-2\right)}\)
\(=\dfrac{3+2\sqrt{2}}{3^2-\left(2\sqrt{2}\right)^2}+\dfrac{\sqrt{5}-2}{\left(\sqrt{5}\right)^2-2^2}\)
\(=\dfrac{3+2\sqrt{2}}{1}+\dfrac{\sqrt{5}-2}{1}\)
\(=3+2\sqrt{2}+\sqrt{5}-2\)
\(=2\sqrt{2}+\sqrt{5}+1\)
2) \(\dfrac{1}{\sqrt{3}-\sqrt{7}}+\dfrac{2}{1-\sqrt{7}}\)
\(=\dfrac{\sqrt{3}+\sqrt{7}}{\left(\sqrt{3}+\sqrt{7}\right)\left(\sqrt{3}-\sqrt{7}\right)}+\dfrac{2\cdot\left(1+\sqrt{7}\right)}{\left(1-\sqrt{7}\right)\left(1+\sqrt{7}\right)}\)
\(=\dfrac{\sqrt{3}+\sqrt{7}}{\left(\sqrt{3}\right)^2-\left(\sqrt{7}\right)^2}+\dfrac{2\cdot\left(1+\sqrt{7}\right)}{1^2-\left(\sqrt{7}\right)^2}\)
\(=\dfrac{-\sqrt{3}-\sqrt{7}}{4}-\dfrac{2\cdot\left(1+\sqrt{7}\right)}{6}\)
\(=\dfrac{-\sqrt{3}-\sqrt{7}}{4}-\dfrac{1+\sqrt{7}}{3}\)
\(=\dfrac{-3\sqrt{3}-3\sqrt{7}}{12}-\dfrac{4+4\sqrt{7}}{12}\)
\(=\dfrac{-3\sqrt{3}-3\sqrt{7}-4-4\sqrt{7}}{12}\)
\(=\dfrac{-3\sqrt{3}-7\sqrt{7}-4}{12}\)
3) \(\dfrac{a-2\sqrt{a}}{2-\sqrt{a}}\)
\(=-\dfrac{a-2\sqrt{a}}{\sqrt{a}-2}\)
\(=-\dfrac{\sqrt{a}\cdot\left(\sqrt{a}-2\right)}{\sqrt{a}-2}\)
\(=-\sqrt{a}\)
4) \(\dfrac{x\sqrt{y}+y\sqrt{x}}{\sqrt{x}+\sqrt{y}}\)
\(=\dfrac{\sqrt{x}\cdot\sqrt{xy}+\sqrt{y}\cdot\sqrt{xy}}{\sqrt{x}+\sqrt{y}}\)
\(=\dfrac{\sqrt{xy}\cdot\left(\sqrt{x}+\sqrt{y}\right)}{\sqrt{x}+\sqrt{y}}\)
\(=\sqrt{xy}\)
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Tính
a, (-2/3) + 3/4 -(-1/6)+(-2/5)
b, (-2/3) +(-1/5)+ 3/4 - 5/6- (-7/10)
c, 1/2 - (-2/5)+1/3+5/7-(01/6)+(-4/35) +1/41
d, (1/100.99) - (1/99.98)-(1/98.97)-...-(1,3.2)- (1/2.1)
1. THỰC HIỆN PHÉP TÍNH :
a) -2/3+3/4--1/6+-2/5 ;
b) -2/3+-1/5+3/4-5/6- -7/10 ;
c)1/2- -2/5+1/3+5/7- -1/6+-4/35+1/41 ;
d) 1/100.99-1/99.98-1/98.97-...-1/3.2-1/2.1
a; - \(\dfrac{2}{3}\) + \(\dfrac{3}{4}\) - (- \(\dfrac{1}{6}\)) + (- \(\dfrac{2}{5}\))
= - \(\dfrac{2}{3}\) + \(\dfrac{3}{4}\) + \(\dfrac{1}{6}\) - \(\dfrac{2}{5}\)
= \(-\dfrac{40}{60}\) + \(\dfrac{45}{60}\) + \(\dfrac{10}{60}\) - \(\dfrac{24}{60}\)
= \(\dfrac{5}{60}\) + \(\dfrac{10}{60}\) - \(\dfrac{24}{60}\)
= \(\dfrac{15}{60}\) - \(\dfrac{24}{60}\)
= - \(\dfrac{3}{20}\)
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b; (- \(\dfrac{2}{3}\)) + (- \(\dfrac{1}{5}\)) + \(\dfrac{3}{4}\) - \(\dfrac{5}{6}\) - \(\dfrac{-7}{10}\)
= - \(\dfrac{2}{3}\) - \(\dfrac{1}{5}\) + \(\dfrac{3}{4}\) - \(\dfrac{5}{6}\) + \(\dfrac{7}{10}\)
= - \(\dfrac{40}{60}\) - \(\dfrac{12}{60}\) + \(\dfrac{45}{60}\) - \(\dfrac{50}{60}\) + \(\dfrac{42}{60}\)
= - \(\dfrac{52}{60}\) + \(\dfrac{45}{60}\) - \(\dfrac{50}{60}\) + \(\dfrac{42}{60}\)
= - \(\dfrac{7}{60}\) - \(\dfrac{50}{60}\) + \(\dfrac{42}{60}\)
= - \(\dfrac{57}{60}\) + \(\dfrac{42}{60}\)
= - \(\dfrac{1}{4}\)
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+ d; \(\dfrac{1}{100.99}\) - \(\dfrac{1}{99.98}\) - \(\dfrac{1}{98.97}\) - ... - \(\dfrac{1}{3.2}\) - \(\dfrac{1}{2.1}\)
= \(\dfrac{1}{100.99}\) - (\(\dfrac{1}{99.98}\) + \(\dfrac{1}{98.97}\) + ... + \(\dfrac{1}{3.2}\) + \(\dfrac{1}{2.1}\))
= \(\dfrac{1}{100.99}\) - (\(\dfrac{1}{1.2}\) + \(\dfrac{1}{2.3}\) + \(\dfrac{1}{3.4}\) + ... + \(\dfrac{1}{98.97}\) + \(\dfrac{1}{98.99}\))
= \(\dfrac{1}{100.99}\) - (\(\dfrac{1}{1}\) - \(\dfrac{1}{2}\) + \(\dfrac{1}{2}\) - \(\dfrac{1}{3}\) + \(\dfrac{1}{3}\) - \(\dfrac{1}{4}\) + ...+ \(\dfrac{1}{98}\) - \(\dfrac{1}{97}\) + \(\dfrac{1}{98}\) - \(\dfrac{1}{99}\))
= \(\dfrac{1}{100.99}\) - (\(\dfrac{1}{1}\) - \(\dfrac{1}{99}\))
= \(\dfrac{1}{100.99}\) - \(\dfrac{98}{99}\)
= - \(\dfrac{9799}{9900}\)
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1. So sánh
A=9024016. ; B=9024000
2. Cho tập hợp A các số tự nhiên lẻ 6<x<11 bằng 2 cách. Tập hợp A có bao nhiêu phần tử?
3. Tính
61+243+39 ; 32.47+32.53. ; 204:[189-(23-6)]. ; 25.{32.[12:4+4(16:2^3)]}
3^7:3^5+5^2.1^2004
4. Tìm x
(x-2):3=2.3^2. ; 3^x-1=27. ; 70-5:(x-3)=5.3 ; (x-2)^2=16
Bài 1 tào lao quá, đương nhiên A > B
Bài 2:
Cách 1: A={7;9}
Cách 2: A={x\(\in\)N|x\(\notin\)Ư(2)|6<x<11|
A có 2 phần tử
Làm từ từ chút
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Tìm x, biết: a) 26.3/4 + x= 30 b) x - 2.1/3 = 1.1/6 c) 8.2/3-x=7.1/4 Em đang cần gấp ạ
a: =>78/4+x=30
=>x=30-78/4=42/4=10,5
b: =>x-2/3=1/6
=>x=1/6+2/3=5/6
c: =>16/3-x=7/4
=>x=16/3-7/4=43/12
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Viết các biểu thức sau dưới đang lũy thừa của một số hữu tỉ:
25.5^3.1/625.5^2. b)4.32:(2^3.1/16). c)5^2.3^5.(3/5)^2. d)(1/7)^2.1/7.49^2
lười quá, thầy cũng cho mấy dạng này lười đánh máy quá
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