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\(\left\{{}\begin{matrix}\left\{{}\begin{matrix}3x-15=45\Leftrightarrow3x=60\Leftrightarrow x=20\\35-5x=50\Leftrightarrow5x=-15\Leftrightarrow x=-3\end{matrix}\right.\\\left\{{}\begin{matrix}\left(2x-5\right)+17=6\Leftrightarrow2x+5=-11\Leftrightarrow2x=-16\Leftrightarrow x=-8\\10-2\left(4-3x\right)=-4\Leftrightarrow8-6x=14\Leftrightarrow6x=-6\Leftrightarrow x=-1\end{matrix}\right.\\\left\{{}\begin{matrix}-12+3\left(-x+7\right)=-18\Leftrightarrow-3x+21=-6\Leftrightarrow-3x=-27\Leftrightarrow x=9\\24:\left(3x-2\right)=-3\Leftrightarrow3x-2=-8\Leftrightarrow3x=-6\Leftrightarrow x=-2\end{matrix}\right.\\-45:5\left(-3-2x\right)=3\Leftrightarrow-15-10x=-15\Leftrightarrow10x=0\Leftrightarrow x=0\end{matrix}\right.\)
Câu 1:
=>5x=15
hay x=3
Câu 2:
\(\Leftrightarrow120-\left(3x+9\right)=12\)
=>3x+9=108
=>3x=99
hay x=33
1) 35.18-5.7.28
=630-5.7.28
= 630-980
=630+(-980)
=-(980-630)
=-350
\(\dfrac{15^2\cdot16^4-15^3\cdot16^3}{12^2\cdot20^3-20^2\cdot12^3}\)
\(=\dfrac{15^2\cdot16^3\left(16-15\right)}{12^2\cdot20^2\left(20-12\right)}\)
\(=\dfrac{3^2\cdot5^2\cdot2^{12}}{2^4\cdot3^2\cdot2^4\cdot5^2\cdot2^3}\)
\(=\dfrac{2^{12}}{2^{11}}=2^1=2\)
\(1-\frac{1}{2}+2-\frac{2}{3}+3-\frac{3}{4}+4-\frac{1}{4}-3-\frac{1}{3}-2-\frac{1}{2}-1\)
\(\left(1-1\right)-\left(\frac{1}{2}+\frac{1}{2}\right)+\left(2-2\right)-\left(\frac{2}{3}+\frac{1}{3}\right)+\left(3-3\right)-\left(\frac{3}{4}+\frac{1}{4}\right)-1\)
\(-1-1-1+4=1\)
MIK XIN LỖI BN NHA VÌ ĐÁNH MÁY HƠI LÂU NHA !! CHÚC BN HOK TỐT NHAA
\(D=\frac{3}{2}+\frac{3}{6}+\frac{3}{12}+...+\frac{3}{90}\)
\(D=\frac{3}{1.2}+\frac{3}{2.3}+\frac{3}{3.4}+...+\frac{3}{9.10}\)
\(D=3.\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{9}-\frac{1}{10}\right)\)
\(D=3.\left(1-\frac{1}{10}\right)=3.\frac{9}{10}=\frac{27}{10}\)
3/1.2 + 3/2.3 + 3/3.4 + 3/4.5 + 3/6.7 hả
thiếu 3/5.6