13+42=
ai nhanh tick nhé
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(26 + 53 ) +(42 -26-55-53)
=79 + ( 16 -55 - 53 )
=79 + (-39-53)
=79 -39 - 53
=40 - 53 = -13
TL :
Vì 42 , 90 chia hết cho x nên x e ƯCLN ( 42 , 90 )
Ta có :
42 = 2 . 3 . 7
90 = 2 . 32 . 5
ƯCLN ( 42 , 90 ) = 2 . 3 = 6
vậy x = 6
\(\frac{11}{13}-\left(\frac{5}{42}-x\right)=\frac{113}{364}\)
\(\left(\frac{5}{42}-x\right)=\frac{11}{13}-\frac{113}{364}\)
\(\left(\frac{5}{42}-x\right)=\frac{15}{28}\)
\(x=\frac{5}{42}-\frac{15}{28}\)
\(x=-\frac{5}{12}\)
vậy \(x=-\frac{5}{12}\)
17 x 42 + 67 x 58 - 50 x 28
= 714 + 3886 - 1400
= 4600 - 1400
= 3200
5/2+13/6+25/12+41/20+61/30+85/42
=2+1/2+2+1/6+2+1/12+2+1/20+2+1/30+2+1/42
=12+(1/2+1/6+1/12+1/20+1/30+1/42)
=12+(1/1.2+1/2.3+1/3.4+1/4.5+1/5.6+1/6.7)
=12+(1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7)
=12+1-1/7
=90/7
5/2+13/6+25/12+41/20+61/30+85/42
=2+1/2+2+1/6+2+1/12+2+1/20+2+1/30+2+1/42
=12+(1/2+1/6+1/12+1/20+1/30+1/42)
=12+(1/1.2+1/2.3+1/3.4+1/4.5+1/5.6+1/6.7)
=12+(1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7)
=12+1-1/7
=90/7
\(\frac{7}{5}-\frac{13}{49}=\frac{343}{245}-\frac{65}{245}=\frac{278}{245}\)
a, \(6.x.5.\left(x-2\right)=23\)
\(\Leftrightarrow30x.\left(x-2\right)=23\)
\(\Leftrightarrow\orbr{\begin{cases}30x=1\\x-20=23\end{cases}\Leftrightarrow\orbr{\begin{cases}x=\frac{1}{30}\\x=43\end{cases}}\left(1\right)}\)
\(\Leftrightarrow\orbr{\begin{cases}30x=23\\x-20=1\end{cases}\Leftrightarrow\orbr{\begin{cases}x=\frac{23}{30}\\x=21\end{cases}\left(2\right)}}\)
\(\Leftrightarrow\orbr{\begin{cases}30x=-1\\x-20=-23\end{cases}\Leftrightarrow\orbr{\begin{cases}x=-\frac{1}{30}\\x=-3\end{cases}}\left(3\right)}\)
\(\Leftrightarrow\orbr{\begin{cases}30x=-23\\x-20=-1\end{cases}\Leftrightarrow\orbr{\begin{cases}x=-\frac{23}{30}\\x=19\end{cases}}}\)
b, \(42-\left(2x+32\right)+12:2=6\)
\(\Leftrightarrow42-\left(2x+32\right)+6=6\)
\(\Leftrightarrow42-\left(2x+32\right)=0\)
\(\Leftrightarrow2x-32=42\)
\(\Leftrightarrow2x=74\)
\(\Leftrightarrow x=37\)
x+(x+1) +(x+2) + ... + (x+14 )=14
(x+x+x+...+x) + (1+2+3+4+ ...+14)=14
15x + [(14-1):1+1].(1+14) :2=14
15x + 105=14
15x=-91
suy ra x=-91/15
341*67+341*16+659*13
=341*(67+16)+659*83
=341*83+659*83
=(341+659)*83
=1000*83
=83000
chắc thế chúc bạn học tốt =)
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