305 480-165 389: 7
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3x7 + 5 = 389
3x7 = 389 - 5
3x7 = 384
x7 = 384 : 3
x7 = 128
x7 = 27
x = 2
\(3.x^7+5=389\)
\(\Rightarrow3.x^7=384\)
\(\Rightarrow x^7=128\)
\(\Rightarrow x^7=2^7\)
\(\Rightarrow x=2\)
Vậy \(x=2\)
b = ( 1+2-3-4) + ( 5+6-7-8) + .............. + (301+302-303-304) + (305 +305)
b = -4 + (-4) + ..................+ (-4) + 610
b= -4 x 76 + 610
b= -304 + 610
b= 306
a.
\(4\times183\times25=4\times25\times183=100\times183=18300\)
b.
\(165\times59+165\times165\times40=165\times\left(59+1+40\right)=165\times100=16500\)
c.
\(56\times49:7=56\times\left(49:7\right)=56\times7=392\)
d.
\(67\times15-57\times15=15\times\left(67-57\right)=15\times10=150\)
\(\left(x-305\right)\times7=26728+19640\\ \left(x-305\right)\times7=46368\\ x-305=46368:7\\ x-305=6624\\ x=6624+305\\ x=6929\)
=480:[75+(49-8.3):5]+1
=480:[75+(49-24):5]+1
=480:[75+25:5]+1
=480:[75+5]+1
=480:80+1
=6+1
=7
1: =1/5-1/4=-1/20
2: =6/8-7/8=-1/8
3: =11/18-14/18=-3/18=-1/6
4: =-28/210+90/210+28/210=3/7
5: =-8/17-34/17=-42/17
1)\(\dfrac{1}{5}+\dfrac{-1}{-4}=\dfrac{4}{20}+\dfrac{5}{20}=\dfrac{9}{20}\)
\(\)2)\(\dfrac{3}{4}+\dfrac{-7}{8}=\dfrac{6}{8}+\dfrac{-7}{8}=\dfrac{-1}{8}\)
3)\(\dfrac{11}{18}+\dfrac{-7}{9}=\dfrac{11}{18}+\dfrac{-14}{18}=\dfrac{-3}{18}=\dfrac{-1}{6}\)
4)\(\dfrac{2}{-15}+\dfrac{3}{7}+\dfrac{-4}{-30}=\dfrac{-2}{15}+\dfrac{2}{15}+\dfrac{3}{7}=0+\dfrac{3}{7}=\dfrac{3}{7}\)
5)\(\dfrac{8}{-17}+\left(-2\right)=\dfrac{-8}{17}+\dfrac{-34}{17}=\dfrac{-42}{17}\)
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