tính
4x 7/8 =
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1)\(y\times7:5+4\times8=134\)
\(\Leftrightarrow y\times7:5+32=134\)
\(\Leftrightarrow y\times7:5=102\)
\(\Leftrightarrow y\times7=510\)
\(\Leftrightarrow y=72,86\)
2) \(\dfrac{1}{4}:0,25-\dfrac{1}{8}:0,125+\dfrac{1}{2}:0,5-\dfrac{1}{10}\)
\(=0,25:0,25-0,125:0,125+0,5:0,5-\dfrac{1}{10}\)
\(=1-1+1-\dfrac{1}{10}\)
\(=\dfrac{9}{10}\)
Ta có: \(\left(4x-8\right)\left(x^2+6\right)-\left(4x-8\right)\left(x+7\right)+9\left(8-4x\right)\)
\(=\left(4x-8\right)\left(x^2+6\right)-\left(4x-8\right)\left(x+7\right)-9\left(4x-8\right)\)
\(=\left(4x-8\right)\left(x^2+6-x-7-9\right)\)
\(=4\left(x-2\right)\cdot\left(x^2-x-10\right)\)
( 4x - 8 ) . ( x2 + 6 ) - ( 4x - 8 ) . ( x + 7 ) + 9 . ( 8 - 4x )
= (4x - 8 ) . ( x2 + 6 ) - ( 4x - 8 ) . ( x + 7 ) - 9 . (4x - 8)
= (4x-8) ( x2+6 - x - 7 - 9)
= 4(x-2)(x^2 -x - 10)
a) 405 - 15 x 2
= 405 - 30
= 375
b) 28 x 64 + 28 x 36
= 28 x ( 64 + 36 )
= 28 x 100
= 2800
c) ( -17 + ( -8 ) + 17 + ( -3 )
= [ ( -17 ) + 17 ] + [ ( -8 ) + ( -3 ) ]
= 0 + ( -11 )
= -11
d) 235 - 4 x { 20 + [ 72 : ( 23 - 1 ) ] }
= 235 - 4 x { 20 + [ 49 : ( 8 - 1 ) ] }
= 235 - 4 x { 20 + [ 49 : 7 ] }
= 235 - 4 x { 20 + 7 }
= 235 - 4 x 27
= 235 - 108
= 127
e) 8 - ( 3 - 7 )
= 8 - 3 + 7
= 5 + 7
= 12
g) 9 - ( -7 ) - 3
= 9 + 7 - 3
= 16 - 3
= 13
f) ( -5 ) - ( 9 - 12 )
= ( -5 ) - 9 +12
= -14 + 12
= -2
a, \(\dfrac{x}{2}+\dfrac{3x}{4}=\dfrac{4}{5}\Leftrightarrow\dfrac{10x+15x}{20}=\dfrac{16}{20}\Rightarrow25x=16\Leftrightarrow x=\dfrac{16}{25}\)
b, \(\dfrac{3}{7}.\dfrac{5}{8}-\dfrac{3}{8}.\dfrac{13}{8}+\dfrac{1}{7}=\dfrac{15}{56}-\dfrac{39}{64}+\dfrac{1}{7}\)
\(=\dfrac{120}{448}-\dfrac{273}{448}+\dfrac{64}{448}=-\dfrac{89}{448}\)
Giải đáp
4 x 7/8
= 21/8
Học tốt
\(=\frac{21}{8}\)