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a: =-12,45+12,45+23,4=23,4
b: =32,18-32,18-14,6+14,6+4,125=4,125
c: =4,5(-12,25-17,75)
=-4,5*30=-135
d: =3,4(-23,68-45,12-31,2)
=3,4*(-100)=-340

\(3^2.x+2^3-4,5+3\frac{1}{2}x=16x+2^3-4,5-15x+6,2.\)
\(\Leftrightarrow9x+8-4,5+\frac{7}{2}x=16x+8-4,5-15x+6,2\)
\(\Leftrightarrow9x+\frac{7}{2}x-16x+15x=8-4,5+6,2-8+4,5\)
\(\Leftrightarrow11,5x=6,2\)
\(\Leftrightarrow x=\frac{62}{115}\)

A=1,25+2,75+4,25+........+17,75+19,25
A có ( 19,25 - 1,25 ) : 1,5 + 1 = 13 số hạng.
A = ( 19,25 + 1,25 ) . 13 : 2
A = 133,25
B = 5,8 . ( 168 - 100 ) + ( 4,5 + 1,3) . ( 15 + 26) + (7,3 - 1,5 )
B = 5,8 . 68 + 5,8 + 5,8
B = 5,8 ( 68 + 1 + 1 )
B = 5,8 . 70
B = 406
\(C=\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}\)
\(C=\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}\)
\(C=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}\)
\(C=\frac{1}{2}-\frac{1}{8}\)
\(C=\frac{3}{8}\)




( 4,5 - 2x ) : 3/4 = 1 1/3
=> 4,5 - 2x = 4/3 . 3/4
=> 4,5 - 2x = 1
=> 2x = 4,5 - 1
=> 2x = 3,5
=> x = 3,5 : 2
=> x = 7/4

\(\left(4,5-2x\right):\frac{3}{4}=1\frac{1}{3}\)
\(\Leftrightarrow\left(4,5-2x\right):\frac{3}{4}=\frac{4}{3}\)
\(\Leftrightarrow4,5-2x=1\)
\(\Leftrightarrow2x=3,5\)
\(\Leftrightarrow x=1,75\)

Ta có : 4,5 - 2x * 147 = 11/14 .
⇒ 9/2 - 2x * 147 = 11/14 .
⇒ 2x * 147 = 9/2 - 11/14 .
⇒ 2x * 147 = 63/14 - 11/14 .
⇒ 2x * 147 = 26/7 .
⇒ 2x = 26/7 : 147 .
⇒ 2x = ( 26 * 147 ) / 7 .
⇒ 2x = 78 .
⇒ x = 78 : 2 .
⇒ x = 39 .
Vậy x = 39 .
\(4,5-2x\cdot147=\dfrac{11}{14}\\ 2x\cdot147=4,5-\dfrac{11}{14}\\ 2x\cdot147=\dfrac{52}{14}\\ 2x=\dfrac{52}{14}:147\\ 2x=\dfrac{26}{1029}\\ x=\dfrac{26}{1029}:2\\ x=\dfrac{13}{1029}\\ Vậy...\)
\(\left(-12,25\right)\cdot4,5+4,5\cdot\left(-17,75\right)\\ =4,5\cdot\left[\left(-12,25\right)+\left(-17,75\right)\right]\\ =4,5\cdot\left[-30\right]=-135\)
(-12,25).4,5+4,5.(-17,75)
=4,5.[-12.25+(-17,75)
=4,5.(-30)
=-135