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(6x-3³).5³=3.5⁴
(6x-27).125=1875
6x-27=1875:125
6x-27=15
6x=15+27
6x=42
x=42:6
x=7
a) 3A = 3. ( 30 + 31 + 32 +...+ 311)
3A = 31 + 32 +33 +....+ 312
3A - A = 31 +32+33 +...+312 - 30 - 31-32- ...- 311
2A = 312 -1
A = (312 -1) : 2
b) A = ( 30 + 31 + 32 33) + .... + ( 38 + 39 + 310 + 311)
A = 40 + ... + 38 . ( 30 + 31 +32 +33)
A = 40 + ... + 38 .40
A = 40 . ( 1 + ...+ 38)
Vì 40 chia hết cho 40
=> 40. ( 1 + ...+38) chia hết cho 40
Vậy A chia hết cho 40
\(a,-\frac{9}{12}=-\frac{9:3}{12:3}=-\frac{3}{4}\)
\(\frac{-18}{-24}=\frac{\left(-18\right):\left(-6\right)}{\left(-24\right):\left(-6\right)}=\frac{3}{4}\)
\(-\frac{35}{70}=-\frac{35:35}{70:35}=\frac{1}{2}\)
\(-\frac{9}{27}=-\frac{9:9}{27:9}=-\frac{1}{3}\)
\(b,\frac{1313}{4242}=\frac{1313:101}{4242:101}=\frac{13}{42}\)
\(\frac{-353535}{-424242}=\frac{\left(-353535\right):\left(-70707\right)}{\left(-424242\right):\left(-70707\right)}=\frac{5}{6}\)
\(c,\frac{2^3\times4^3\times5^4}{8^2\times25^3\times7}=\frac{2^3\times4^3\times25^2}{8\times8^2\times25^2\times25\times7}\) ( 4^3 = 8^2 ; 5^4 = 25^2 )
\(=\frac{1}{25\times7}=\frac{1}{175}\)
\(a.\frac{-9}{-12}=\frac{-9:3}{-12:3}=\frac{-3}{-4}.\)
\(\frac{-18}{-24}=\frac{-18:6}{-24:6}=\frac{-3}{-4}\)
\(\frac{-35}{-70}=\frac{-35:35}{-70:35}=\frac{-1}{-2}\)
\(\frac{-9}{-27}=\frac{-9:9}{-27:9}=\frac{-1}{-3}\)
1 +( -2) + 3 + (-4) +...+2001 + (-2002) + 2003
= [1 +( -2)] + [3 + (-4)] +...+ [-2000+2001] + [(-2002) + 2003]
= -1 + -1 +............ + 1 + 1
= 0
B x 3 = 1x2x3 + 2x3x3 + 3x4x3 + 4x5x3 + ... + 99x100x3
= 1x2x3 + 2x3x(4-1) + 3x4x(5-2) + 4x5x(6-3) + ... + 99x100x(101-98)
= 1x2x3 + 2x3x4 - 1x2x3 + 3x4x5 - 2x3x4 + 4x5x6 - 3x4x5 + ... + 99x100x101 - 98x99x100.
= 99x100x101
B = 99x100x101 : 3
= 333300
nhanh k minh
B= 1x2+3x4+5x6+...+99x100
=> Bx3= 1x2x3 + 2x3x3 + 3x4x3 + 4x5x3 + ...+ 99x100x3
=> Bx3= 1x2x3 + 2x3x(4-1) + 3x4x(5-2) + 4x5x(6-3)+...+99x100x(101-98)
=> Bx3= 1x2x3 + 2x3x4 - 1x2x3 + 3x4x5 - 2x3x4 +4x5x6 - 3x4x5 +...+ 99x100x101 - 98x99x100
=> Bx3= 99x100x101
=> B= 99x100x101:3
=> B= 333300
\(-12+x=5x-20\)
\(-12+20=5x-x=4x\)
\(\Rightarrow8=4x\)
\(\Leftrightarrow x=2\)
12x+3.23=23.x-4.32
12x+3.8=8.x-4.9
12x+24=8x-36
12x-8x=36-24
4x=12
x=12:4=3
B = 1434:{[(216+184:8).3]}
B = 1434:{[239.3]}
B = 1434 : 717
B = 2
\(B=1434:\left\{\left[\left(216+184:8\right).3\right]\right\}\)
\(B=1434:\left\{\left[216+23\right].3\right\}\)
\(B=1434:\left(239.3\right)\)
\(B=1434:717\)
\(B=2\)
(Tíck cho mình với nhá!)