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a) 410 x 230 = (22)10 x 230 = 220 x 230 = 250
b) 925.274.813= (32)25.(33)4.(34)3= 350.312.312= 374
c) 2550.1255= (52)50.(53)5 = 5100.515= 5115
d) 643.48.64= (26)3.(22)8. (2.3)4 = 218.216.24.34=238.81
1, 15-(2x-3)=6
<=>2x-3=15-6
<=>2x=15-6+3
<=>2x=12
<=>x=12:2
<=>x=6
Vậy x=6
2, (x-2).3=3\(^2\)
<=>x-2=3\(^2\):3
<=>x-2=9:3
<=>x=9:3-2
<=>x=1
vậy x=1
3, (x+7)-25=13
<=>x+7=13+25
<=>x=13+25-7
<=>x=31
Vậy x=31
4, 450:(x-190)=50
<=>x-190=450:50
<=>x=450:50+/ 190
<=>x=199
Vậy x=199
5, 3 \(^x\)x 2=18
<=>3\(^x\)=18:2
<=>3\(^x\)=9=3\(^2\)
=>x=2
vậy x=2
\(A=\frac{1\cdot2+2\cdot4+3\cdot6+4\cdot8+5\cdot10+6\cdot12}{3\cdot4+6\cdot8+9\cdot12+12\cdot16+15\cdot20+18\cdot24}\)
\(A=\frac{2\cdot3\left[1\cdot2\right]+2\cdot3\left[2\cdot4\right]+2\cdot3\left[3\cdot6\right]+2\cdot3\left[4\cdot8\right]+2\cdot3\left[5\cdot10\right]}{3\cdot4\left[3\cdot4+6\cdot8+9\cdot12+12\cdot16+15\cdot20\right]}\)
\(A=\frac{\left[3\cdot4+6\cdot8+9\cdot12+12\cdot16+15\cdot20\right]}{2\cdot3\left[3\cdot4+6\cdot8+9\cdot12+12\cdot16+15\cdot20\right]}=\frac{1}{2\cdot3}=\frac{1}{6}\)
https://www.youtube.com/channel/UC5odkiOvzz9Rvu3HUYlL2IQ?view_as=subscriber
[ 25( 18 - 42 ) - 10 ] : 4 + 6
= [ 25( 18 - 16 ) - 10 ] : 4 + 6
= [ 25 . 2 - 10 ] : 4 + 6
= 40 : 4 + 6
= 16
{25.(18-4^2)-10}:4+6
={25.(18-16)-10}:4+6
=(25.2-10):4+6
=(50-10):4+6
=40:4+6
=10+6
=16