a/b x 3/4 + 2/5 = 2
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![](https://rs.olm.vn/images/avt/0.png?1311)
Bài 1
a) 3 2/5 - 1/2
= 17/5 - 1/2
= 34/10 - 5/10
= 29/10
b) 4/5 + 1/5 × 3/4
= 4/5 + 3/20
= 16/20 + 3/20
= 19/20
c) 3 1/2 × 1 1/7
= 7/2 × 8/7
= 4
d) 4 1/6 : 2 1/3
= 25/6 : 7/3
= 25/14
Bài 2
a) 3 × 1/2 + 1/4 × 1/3
= 3/2 + 1/12
= 18/12 + 1/12
= 19/12
b) 1 4/5 - 2/3 : 2 1/3
= 9/5 - 2/3 : 7/3
= 9/5 - 2/7
= 63/35 - 10/35
= 53/35
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a | b | c | a x (b + c) | a x b + a x c |
---|---|---|---|---|
4 | 5 | 2 | 4 x (5 + 2) = 28 | 4 x 5 + 4 x 2 = 28 |
3 | 4 | 5 | 3 x (4 + 5) = 27 | 3 x 4 + 3 x 5 = 27 |
6 | 2 | 3 | 6 x (2 + 3) = 30 | 6 x 2 + 6 x 3 = 30 |
a | b | c | a x ( b + c ) | a x b + a x c |
4 | 5 | 2 | 4 x ( 5 + 2 ) = 28 | 4 x 5 + 4 x 2 = 28 |
3 | 4 | 5 | 3 x ( 4 + 5 ) = 27 | 3 x 4 + 3 x 5 = 27 |
6 | 2 | 3 | 6 x ( 2 + 3 ) = 30 | 6 x 2 + 6 x 3 = 30 |
![](https://rs.olm.vn/images/avt/0.png?1311)
a | b | c | a x (b + c) | a x b + a x c |
---|---|---|---|---|
4 | 5 | 2 | 4 x (5 + 2) = 28 | 4 x 5 + 4 x 2 = 28 |
3 | 4 | 5 | 3 x (4 + 5) = 27 | 3 x 4 + 3 x 5 = 27 |
6 | 2 | 3 | 6 x (2 + 3) = 30 | 6 x 2 + 6 x 3 = 30 |
![](https://rs.olm.vn/images/avt/0.png?1311)
a) \(=5x^2+40x+80+4\left(x^2-10x+25\right)-9\left(x+4\right)\left(x-4\right)\)
\(=5x^2+40x+80+4x^2-40x+100-9x^2+144\)
\(=9x^2-9x^2+40x-40x+324\)
\(=324\)
b) \(=x^2+4xy+4y^2+4x^2-4xy+y^2-5x^2+5y^2-10y^2+90\)
\(=5x^2-5x^2+10y^2-10y^2+\left(4xy-4xy\right)+90\)
\(=90\)
c)
\(=a^2+b^2+c^2+2\left(ab+bc+ca\right)+a^2+b^2+c^2+2ab-2ac-2bc-2a^2-4ab-2b^2\)
\(=\left(2a^2-2a^2\right)+\left(2b^2-2b^2\right)+2c^2+4ab-4ab+2\left(ac+bc-ac-bc\right)\)
\(=2c^2\)
a) 5( x + 4 )2 + 4( x - 5 )2 - 9( 4 + x )( x - 4 )
= 5( x2 + 8x + 16 ) + 4( x2 - 10x + 25 ) - 9( x2 - 16 )
= 5x2 + 40x + 80 + 4x2 - 40x + 100 - 9x2 + 144
= ( 5x2 + 4x2 - 9x2 ) + ( 40x - 40x ) + ( 80 + 100 + 144 )
= 324
b) ( x + 2y )2 + ( 2x - y )2 - 5( x + y )( x - y ) - 10( y + 3 )( y - 3 )
= x2 + 4xy + 4y2 + 4x2 - 4xy + y2 - 5( x2 - y2 ) - 10( y2 - 9 )
= x2 + 4xy + 4y2 + 4x2 - 4xy + y2 - 5x2 + 5y2 - 10y2 + 90
= ( x2 + 4x2 - 5x2 ) + ( 4xy - 4xy ) + ( 4x2 + y2 + 5y2 - 10y2 ) + 90
= 90
c) ( a + b + c )2 + ( a + b - c )2 - 2( a + b )2
= [ ( a + b ) + c ]2 + [ ( a + b ) - c ]2 - 2( a + b )2
= ( a + b )2 + 2( a + b )c + c2 + ( a + b )2 - 2( a + b )c + c2 - 2( a + b )2
= [ ( a + b )2 + ( a + b )2 - 2( a + b )2 ] + [ 2( a + b )c - 2( a + b )c ] + ( c2 + c2 )
= 2c2
![](https://rs.olm.vn/images/avt/0.png?1311)
a: 3/7x4/5=12/35
2/5+3/4=8/20+15/20=23/20
b: 2/5:4=2/20=1/10
1/4+2=9/4
c: 2/5:2/3=3/5
2/3-3/8=16/24-9/24=7/24
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\begin{array}{l}a)A = 3x - 4{x^4} + {x^3}\\ = - 4{x^4} + {x^3} + 3x\\b)B = - 2{x^3} - 5{x^2} + 2{x^3} + 4x + {x^2} - 5\\ = ( - 2{x^3} + 2{x^3}) + \left( { - 5{x^2} + {x^2}} \right) + 4x - 5\\ = 0 + ( - 4{x^2}) + 4x - 5\\ = - 4{x^2} + 4x - 5\\c)C = {x^5} - \dfrac{1}{2}{x^3} + \dfrac{3}{4}x - {x^5} + 6{x^2} - 2\\ = \left( {{x^5} - {x^5}} \right) - \dfrac{1}{2}{x^3} + 6{x^2} + \dfrac{3}{4}x - 2\\ = - \dfrac{1}{2}{x^3} + 6{x^2} + \dfrac{3}{4}x - 2\end{array}\)
32/15