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A=55/11.16+55/16.21+55/21.26+55/26.31+55/31.36+55/36.41
=11.(5/11.16+5/16.21+...+5/36.41)
=11.(1/11-1/16+1/16-1/21+...+1/36-1/41)
=11.(1/11-1/41)
=11.30/451
=30/41
\(\dfrac{11}{6}+\dfrac{1}{4}=\dfrac{22}{12}+\dfrac{3}{12}=\dfrac{25}{12}\)
\(\dfrac{2}{5}-\dfrac{3}{8}=\dfrac{16}{40}-\dfrac{15}{40}=\dfrac{1}{40}\)
\(\dfrac{3}{10}-\dfrac{4}{15}=\dfrac{9}{30}-\dfrac{8}{30}=\dfrac{1}{30}\)
\(3+\dfrac{2}{5}=\dfrac{15}{5}+\dfrac{2}{5}=\dfrac{17}{5}\)
\(\dfrac{333}{777}+\dfrac{22}{55}=\dfrac{3}{7}+\dfrac{2}{5}=\dfrac{15}{35}+\dfrac{14}{35}=\dfrac{29}{35}\)
1: \(\dfrac{-7}{4}\cdot\dfrac{2}{9}=\dfrac{-14}{36}=\dfrac{-7}{18}\)
2: \(=\dfrac{12}{13}\cdot\dfrac{26}{5}=\dfrac{24}{5}\)
3: \(=\dfrac{20}{11}\cdot\dfrac{55}{21}=\dfrac{100}{21}\)
4: \(=\dfrac{-40}{240}=\dfrac{-1}{6}\)
Bài 1:
1) Ta có: \(\left(-12\right)+6\cdot\left(-3\right)\)
\(=-12-18\)
=-30
2) Ta có: \(\left(36-2020\right)+\left(2019-136\right)-27\)
\(=36-2020+2019-136-27\)
\(=1-100-27\)
\(=-126\)
3) Ta có: \(\left(144-97\right)-\left(244-197\right)\)
\(=144-97-244+197\)
\(=-100+100=0\)
4) Ta có: \(\left(-24\right)\cdot13-24\cdot\left(-3\right)\)
\(=-24\cdot13+24\cdot3\)
\(=24\cdot\left(-13+3\right)\)
\(=24\cdot\left(-10\right)=-240\)
5) Ta có: \(54+55+56+57+58-\left(64+65+66+67+68\right)\)
\(=54+55+56+57+58-64-65-66-67-68\)
\(=\left(54-64\right)+\left(55-65\right)+\left(56-66\right)+\left(57-67\right)+\left(58-68\right)\)
\(=\left(-10\right)+\left(-10\right)+\left(-10\right)+\left(-10\right)+\left(-10\right)\)
=-50
6) Ta có: \(24\cdot\left(16-5\right)-16\cdot\left(24-5\right)\)
\(=24\cdot16-24\cdot5-16\cdot24+16\cdot5\)
\(=-24\cdot5+16\cdot5\)
\(=5\cdot\left(-24+16\right)\)
\(=-5\cdot8=-40\)
7) Ta có: \(47\cdot\left(23+50\right)-23\cdot\left(47+50\right)\)
\(=47\cdot23+47\cdot50-23\cdot47-23\cdot50\)
\(=47\cdot50-23\cdot50\)
\(=50\cdot\left(47-23\right)\)
\(=50\cdot24=1200\)
8) Ta có: \(\left(-31\right)\cdot47+\left(-31\right)\cdot52+\left(-31\right)\)
\(=-31\cdot\left(47+52+1\right)\)
\(=-31\cdot100=-3100\)
Bài 2:
1) Ta có: \(-17-\left(2x-5\right)=-6\)
\(\Leftrightarrow-17-2x+5+6=0\)
\(\Leftrightarrow-2x-6=0\)
\(\Leftrightarrow-2x=6\)
hay x=-3
Vậy: x=-3
2) Ta có: \(10-2\left(4-3x\right)=-4\)
\(\Leftrightarrow10-8+6x+4=0\)
\(\Leftrightarrow6x+6=0\)
\(\Leftrightarrow6x=-6\)
hay x=-1
Vậy: x=-1
3) Ta có: \(-12+3\left(-x+7\right)=-18\)
\(\Leftrightarrow-12-3x+21+18=0\)
\(\Leftrightarrow-3x+27=0\)
\(\Leftrightarrow-3x=-27\)
hay x=9
Vậy: x=9
4) Ta có: \(-45:\left[5\cdot\left(-3-2x\right)\right]=3\)
\(\Leftrightarrow5\cdot\left(-3-2x\right)=-15\)
\(\Leftrightarrow-2x-3=-3\)
\(\Leftrightarrow-2x=0\)
hay x=0
Vậy: x=0
5) Ta có: x(x+3)=0
\(\Leftrightarrow\left[{}\begin{matrix}x=0\\x+3=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=0\\x=-3\end{matrix}\right.\)
Vậy: \(x\in\left\{0;-3\right\}\)
6) Ta có: (x-2)(x+4)=0
\(\Leftrightarrow\left[{}\begin{matrix}x-2=0\\x+4=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=2\\x=-4\end{matrix}\right.\)
Vậy: \(x\in\left\{2;-4\right\}\)
7) Ta có: \(x\left(x+1\right)\left(x-3\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=0\\x+1=0\\x-3=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=0\\x=-1\\x=3\end{matrix}\right.\)
Vậy: \(x\in\left\{0;-1;3\right\}\)
Bài 1:
1) Ta có: (−12)+6⋅(−3)(−12)+6⋅(−3)
=−12−18=−12−18
=-30
2) Ta có: (36−2020)+(2019−136)−27(36−2020)+(2019−136)−27
=36−2020+2019−136−27=36−2020+2019−136−27
=1−100−27=1−100−27
=−126
Tớ chcs cậu học thật giỏi nha !
Bài 1:
Chiều cao của tam giác là:
12,56 x 2 : 8 = 3,14 (cm)
Đáp số: 3,14 cm
Bài 2:
a) 2 + 5/7 = 2/1 + 5/7 = 14/7 + 5/7 = 19/7
b) 13/5 - 2 = 13/5 - 2/1 = 13/5 - 10/5 = 3/5
c) 1/8 + 3/4 - 1/6 = 3/24 + 18/24 - 6/24 = 17/24
e) 12/5 - 2/2 + 7/7 - 6/6 = 12/5 - 1 + 1 - 1 = 12/5 - 1 = 12/5 - 5/5 = 7/5
Bài 3:
A = 55/11.16 + 55/16.21 + 55/21.26 + 55/26.31 + 55/31.36 + 55/36.41
A = 11.(1/11 - 1/16 + 1/16 - 1/21 + 1/21 - 1/26 + 1/26 - 1/31 + 1/31 - 1/36 + 1/36 - 1/41)
A = 11.(1/11 - 1/41)
A = 11.30/451
A = 30/41
Bài 1 :
Chiều cao tam giác đó là :
\(12,56.2:8=3,14\) ( cm )
Vậy : chiều cao tam giác đó là \(3,14\) cm.
Bài 2 :
a) \(2+\frac{5}{7}=\frac{14}{7}+\frac{5}{7}=\frac{19}{7}\)
b) \(\frac{13}{15}-2=\frac{13}{15}-\frac{30}{15}=-\frac{17}{15}\)
c) \(3-\frac{3}{8}=\frac{24}{8}-\frac{3}{8}=\frac{21}{8}\)
d) \(\frac{1}{8}+\frac{3}{4}-\frac{1}{6}=\left(\frac{1}{8}+\frac{6}{8}\right)-\frac{8}{48}=\frac{7}{8}-\frac{8}{48}=\frac{42}{48}-\frac{8}{48}=\frac{34}{48}=\frac{17}{24}\)
e) \(\frac{12}{5}-\frac{2}{2}+\frac{7}{7}-\frac{6}{6}=\frac{12}{5}-1+1-1=\frac{12}{5}-1=\frac{12}{5}-\frac{5}{5}=\frac{7}{5}\)
Bài 3 :
\(A=\frac{55}{11.16}+\frac{55}{16.21}+\frac{55}{21.26}+....+\frac{55}{36.41}\)
\(\Leftrightarrow A=11.\left(\frac{5}{11.16}+\frac{5}{16.21}+\frac{5}{21.26}+\frac{5}{26.31}+\frac{5}{31.36}+\frac{5}{36.41}\right)\)
\(\Leftrightarrow A=11.\left(\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+\frac{1}{21}-\frac{1}{26}+\frac{1}{26}-\frac{1}{31}+\frac{1}{31}-\frac{1}{36}+136\right)-\frac{1}{41}\)
\(\Leftrightarrow A=11.\left(\frac{1}{11}-\frac{1}{41}\right)=11.\frac{30}{451}=\frac{30}{41}\)
Vậy : \(A=\frac{30}{41}\)