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\(a,\Leftrightarrow x=7-4=3\\ b,\Leftrightarrow2x=-18+5=-13\\ \Leftrightarrow x=-\dfrac{13}{2}\\ c,\Leftrightarrow x-21=10\\ \Leftrightarrow x=31\\ d,\Leftrightarrow-12-x+19=0\\ \Leftrightarrow7-x=0\\ \Leftrightarrow x=7\)
a, <=> x=7-4
<=> x=3
b, 2x= -18 +5
<=>2x=-13
<=> x= -13/2
c, <=> x -21=-10
<=> x= -10 +21
<=> x=11
d, <=> -12+19 -x=0
<=> 7-x=0
<=> x=7
\(250:\left(2x-4x\right)=124\cdot126\)
\(\Leftrightarrow250:\left(-2x\right)=124\cdot126\)
\(\Leftrightarrow-2x=\frac{250}{124\cdot126}=\frac{125}{7812}\)
\(\Leftrightarrow x=-\frac{125}{15624}\)
250: (2x - 4x )=15624
(2x - 4x) = 15624 ÷250
(2x - 4x ) = 62,496
X × (2+4) =62,496
X × 6 = 62,496
x=62,496÷6
X= 10.416
a: \(2x+36:12=5\cdot3\)
\(\Leftrightarrow2x+3=15\)
hay x=6
\(2.53.12+4.6.87-3.8.40\)
\(=2.53.4.3+4.6.87-3.2.4.40\)
\(=4.6.53+4.6.87-4.6.40\)
\(=4.6.\left(53+87-40\right)\)
\(=4.6.100=2400\)
\(\frac{2}{3}+\frac{1}{3}.\left(\frac{-4}{9}+\frac{3}{6}\right):\frac{7}{12}\)
\(=\frac{2}{3}+\frac{1}{3}.\frac{1}{18}:\frac{7}{12}\)
\(=\frac{2}{3}+\frac{1}{54}:\frac{7}{12}\)
\(=\frac{2}{3}+\frac{2}{63}\)
\(=\frac{44}{63}\)
~ Hok tốt ~
a là : 3.15 = 45
\(a\div3=15\\ a=15\cdot3\\ a=45\)