X + 3/10 x X - 2,8 = 6,3 ( X là số chưa biết, x là dấu nhân)
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x+x.2,7+x.6,3=120
x.1+x.2,7+x.6,3=120
x.(1+2,7+6,3)=120
x. 10 =120
x=120:10
x=12
\(\left(84,6-2\cdot x\right):3,02=5,1\)
\(\Rightarrow84,6-2\cdot x=15,402\)
\(\Rightarrow2\cdot x=69,198\)
\(\Rightarrow x=69,198:2\)
\(\Rightarrow x=34,599\)
_____________
\(\left(15\cdot24-x\right):0,25=100:0,25\)
\(\Rightarrow\left(360-x\right):0,25=400\)
\(\Rightarrow360-x=100\)
\(\Rightarrow x-360-100\)
\(\Rightarrow x=260\)
______________
\(128\cdot x-12\cdot x-16\cdot x=5200\)
\(\Rightarrow x\cdot\left(128-12-16\right)=5200\)
\(\Rightarrow x\cdot100=5200\)
\(\Rightarrow x=5200:100\)
\(\Rightarrow x=52\)
__________________
\(5\cdot x+3,75\cdot x+1,25\cdot x=20\)
\(\Rightarrow x\cdot\left(5+3,75+1,25\right)=20\)
\(\Rightarrow10\cdot x=20\)
\(\Rightarrow x=20:10\)
\(\Rightarrow x=2\)
\(x\cdot3,7+x\cdot6,3=360:120\)
\(\Rightarrow x\cdot\left(3,7+6,3\right)=3\)
\(\Rightarrow x\cdot10=3\)
\(\Rightarrow x=\dfrac{3}{10}\)
__________________
\(x\cdot23-6\cdot23+x\cdot69=320\)
\(\Rightarrow x\cdot\left(23+69\right)=320+6\cdot23\)
\(\Rightarrow x\cdot92=458\)
\(\Rightarrow x=458:92\)
\(\Rightarrow x=\dfrac{229}{46}\)
___________________
\(\left(x+1\right)\left(x+2\right)=72\)
\(\Rightarrow x^2+2x+x+2=72\)
\(\Rightarrow x^2+3x+2=72\)
\(\Rightarrow x^2+3x+2-72=0\)
\(\Rightarrow x^2+3x-70=0\)
\(\Rightarrow x^2+10x-7x-70=0\)
\(\Rightarrow\left(x-7\right)\left(x+10\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x=7\\x=-10\end{matrix}\right.\)
___________________
\(\left(x+2\right)\cdot16\cdot x=160x\)
\(\Rightarrow16x^2+32x=160x\)
\(\Rightarrow16x^2+32x-160x=0\)
\(\Rightarrow16x^2-128x=0\)
\(\Rightarrow16x\left(x-8\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x=0\\x=8\end{matrix}\right.\)
X x 1,1 + X : 2,5 = 12
X x 1,1 + X x 0,4 = 12
X x ( 1,1 + 0,4 ) = 12
X x 1,5 = 12
X = 12 : 1,5
X = 8
\(x\times100567=1467171963\)
\(x=1467171963\div100567\)
\(x=14589\)
Vậy x=14589
X x 2, 8 + X x 5, 2 = 48
2X = 48 : ( 2, 8 + 5, 2 )
2X = 6
X = 6 : 2
X = 3
~ Chúc bạn học tốt ~
X x 2,8 + X x 5,2 =48
X x [2,8+5,2] =48
X x 8 =48
X =48:8
X =6
Giải
X + X : 5 x 7,5 + X : 2 x 9 = 315
X + 7,5 X / 5 + 9 X / 2 = 315
X + 1,5 X + 4,5 X = 315
7X = 315
X = 315 : 7
X = 45
Xx1+Xx1:5x7,5+Xx1:2x9=315
Xx1+Xx0,2x7,5+Xx0,5x9=315
Xx1+Xx1,5+Xx4,5=315
Xx(1+1,5+4,5)=315
Xx7=315
X=315:7
X=45
\(\Rightarrow x\times\left(1+\frac{3}{10}\right)=6,3+2,8\)
\(\Rightarrow x\times1,3=9,1\)
\(\Rightarrow x=\frac{9,1}{1,3}\)
\(\Rightarrow x=7\)