Tính giá trị của các biểu thức sau khi bỏ dấu ngoặc: D = - 3 5 + 3 4 - - 3 4 + 2 5
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A= (3,1 - 2,5) - (-2,5 + 3,1)
=3.1-2.5+2.5-3.1
=0
B= (5,3 - 2,8) - (4 + 5,3)
=5.3 - 2.8-4-5.3
= -6.8
C= -(251.3 + 281) + 3.251 - (1-281)
=-251.3-281+3.251-1+281
=-1
D= -(3/5+3/4)−(−3/4+2/5)
= -3/5-3/4+3/4-2/5
= -5/5
=-1
\(A=\left(3,1-2,5\right)-\left(-2,5+3,1\right)=3,1-2,5+2,5-3,1=0\)
\(B=\left(5,3-2,8\right)-\left(4+5,3\right)=5,3-2,8-4-5,3=-6,8\)
\(C=-\left(215\cdot3+281\right)+3\cdot215-\left(1-281\right)=-215\cdot3-281+3\cdot215-1+281=1\)
\(D=-\left(\frac{3}{5}+\frac{3}{4}\right)-\left(-\frac{3}{4}+\frac{2}{5}\right)=-\frac{3}{5}-\frac{3}{4}+\frac{3}{4}-\frac{2}{5}=-1\)
B = (5,3 – 2,8) – (4 + 5,3)
= 5,3 – 2,8 -4 -5,3
= (5,3 – 5,3 ) – (2,8 + 4)
= 0 – 6,8 = -6,8
Cách 2:
\(A=\left(6-\frac{2}{3}+\frac{1}{2}\right)-\left(5+\frac{5}{3}-\frac{3}{2}\right)-\left(3-\frac{7}{3}+\frac{5}{2}\right)\)
\(=\left(\frac{36}{6}-\frac{4}{6}+\frac{3}{6}\right)-\left(\frac{30}{6}+\frac{10}{6}-\frac{9}{6}\right)-\left(\frac{18}{6}-\frac{14}{6}+\frac{15}{6}\right)\)
\(=\frac{36}{6}-\frac{4}{6}+\frac{3}{6}-\frac{30}{6}-\frac{10}{6}+\frac{9}{6}-\frac{18}{6}+\frac{14}{6}-\frac{15}{6}\)
\(=\frac{36-4+3-30-10+9-18+14-15}{6}\)
\(=-\frac{15}{6}=-\frac{5}{2}\)
***** nhá, mất công làm đấy
C1:
\(A=\left(\frac{36}{6}-\frac{4}{6}+\frac{3}{6}\right)-\left(\frac{150}{30}+\frac{50}{30}+\frac{45}{30}\right)-\left(\frac{18}{6}-\frac{14}{6}+\frac{15}{6}\right)\)
\(=\frac{35}{6}-\frac{155}{30}-\frac{19}{6}=\frac{35}{6}-\frac{19}{6}-\frac{155}{30}\)
\(=\frac{16}{6}-\frac{155}{30}=\frac{80}{30}-\frac{155}{30}=\frac{75}{30}=\frac{-5}{2}=-2\frac{1}{2}\)
C2:
\(A=6-\frac{2}{3}+\frac{1}{2}-5-\frac{5}{3}+\frac{3}{2}-3+\frac{7}{3}-\frac{5}{2}\)
\(=\left(6-5-3\right)-\left(\frac{2}{3}+\frac{5}{3}-\frac{7}{3}\right)+\left(\frac{1}{2}+\frac{3}{2}-\frac{5}{2}\right)\)
\(=-2-0+\frac{-1}{2}\)
\(=-2+\frac{-1}{2}=-2\frac{1}{2}\)
Thực hiện phép tính sau:
\(B=\frac{5}{9}.2,\left(37\right)+0,\left(5\right).3,\left(62\right)-2\sqrt{\left(\frac{-2}{3}\right)^2}\)
Cách 1: = ( 36/6 - 4/6 + 3/6 ) - ( 30/6 + 10/6 - 9/6 ) - ( 18/6 - 14/6 + 15/6 )
= 35/6 - 31/6 - 19/6
= -5/2
Cách 2: = 6 - 2/3 + 1/2 - 5 - 5/3 + 3/2 -3 + 7/3 - 5/2
= ( 6 - 5 - 3 ) + ( -2/3 - 5/3 + 7/3 ) + ( 1/2 + 3/2 - 5/2 )
= -2 + 0 + -1/2
= -5/2
Bài 1:
a, \(\dfrac{-x-2}{3}\) = - \(\dfrac{6}{7}\)
- \(x\) - 2 = - \(\dfrac{18}{7}\)
\(x\) = - 2 + \(\dfrac{18}{7}\)
\(x\) = - \(\dfrac{4}{7}\)
Bài b, \(\dfrac{4}{7-x}\) = \(\dfrac{1}{3}\)
12 = 7 - \(x\)
\(x\) = 7 - 12
\(x\) = -5
cách 2:
a=\(6-\frac{2}{3}+\frac{1}{2}-5-\frac{5}{3}+\frac{3}{2}-3+\frac{7}{3}-\frac{5}{2}\)
a=(6-5-3)-(2/3+5/3-7/3)+(1/2+3/2-5/2)
a=-2-1/2
a=-5/2
Cách 1:
A=(3+ 1/2 -2/3 ) -( 2- 2/3 +5/2) - (5- 5/2 + 4/3)
A=17/6-23/6-23/6
A=-29/6
Cách 2:
A=(3+ 1/2 -2/3 ) -( 2- 2/3 +5/2) - (5- 5/2 + 4/3)
A=3+ 1/2 -2/3 - 2+ 2/3 -5/2 - 5+ 5/2 - 4/3
A=-29/6
cách 1:
\(A=\left(3+\frac{1}{2}-\frac{2}{3}\right)-\left(2-\frac{2}{3}+\frac{5}{2}\right)-\left(5-\frac{5}{2}+\frac{4}{3}\right)\)
\(=3+\frac{1}{2}-\frac{2}{3}-2+\frac{2}{3}-\frac{5}{2}-5+\frac{5}{2}-\frac{4}{3}=-4+\frac{1}{2}-\frac{4}{3}\)
\(=\frac{-24}{6}+\frac{3}{6}-\frac{8}{6}=-\frac{29}{6}\)
cách 2:
\(A=\left(3+\frac{1}{2}-\frac{2}{3}\right)-\left(2-\frac{2}{3}+\frac{5}{2}\right)-\left(5-\frac{5}{2}+\frac{4}{3}\right)\)
\(=\left(\frac{18}{6}+\frac{3}{6}-\frac{4}{6}\right)-\left(\frac{12}{6}-\frac{4}{6}+\frac{15}{6}\right)-\left(\frac{30}{6}-\frac{15}{6}+\frac{8}{6}\right)\)
\(=\frac{17}{6}-\frac{23}{6}-\frac{23}{6}=-\frac{29}{6}\)