tính nhanh:48x47-47x47-20-27
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( 27 - 11 ) + ( 20 - 9 - 27 )
= 27 - 11 + 20 - 9 - 27
= (27 - 27) + 20 - (11 + 9)
= 20 - 20 = 0
![](https://rs.olm.vn/images/avt/0.png?1311)
Answer:
Bài 1:
\(\left(1+2x\right)^2+2.\left(1+2x\right).\left(x-1\right)+\left(x-1\right)^2\)
\(=[\left(1+2x\right)+\left(x-1\right)]^2\)
\(=[1+2x+x-1]^2\)
\(=[\left(1-1\right)+\left(2x+x\right)]^2\)
\(=9x^2\)
Bài 2:
\(x^2-6x+7\)
\(=x^2+x-7x-7\)
\(=x.\left(x+1\right)-7.\left(x+1\right)\)
\(=\left(x+1\right).\left(x-7\right)\)
Bài 3:
\(47^2-47.47+37^2\)
\(=47^2-47^2+37^2\)
\(=0+37^2\)
\(=1369\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(20+\left(27+13\right)+\left(14+26\right)\)
\(=20+40+40\)
\(=100\)
![](https://rs.olm.vn/images/avt/0.png?1311)
20 x 45 + 27 x 25 + 27 + 15 x 27
= 20 x 45 + 27 x 25 + 27 x 1 + 15 x 27
= 27 x ( 25 + 1 + 27 ) + 20 x 45
= 27 x 53 + 20 x 45
= 1431 + 900
= 2331
![](https://rs.olm.vn/images/avt/0.png?1311)
`#040911`
`b,`
`6 \times 1235 \times 20 - 5 \times 235 \times 24`
`= 6 \times (1000 + 235) \times 20 - 5 \times 235 \times 24`
`= 120 \times 1000 + 120 \times 235 - 120 \times 235`
`= 120 \times 1000 + 0`
`= 120000`
`c,`
\((145 \times 99+145)-143 \times 101-143\)
`=`\(145 \times 99 + 145 - 143 \times 101 - 143\)
`=`\(145 \times (99 + 1) - 143 \times (101 - 1)\)
`=`\(145 \times 100 - 143 \times 100\)
`=`\(100 \times (145 - 143)\)
`=`\(100 \times 2=200\)
`d,`
`54 \times 47 - 47 \times 53 - 20 - 27`
`= 54 \times 47 - 47 \times 53 - (20 + 27)`
`= 54 \times 47 - 47 \times 53 - 47`
`= 47 \times (54 - 53 - 1)`
`= 47 \times 0=0`
48x47-47x47-20-27
= 48 x 47 - 47 x 47 - 47
= 48 x 47 - 47 x 47 - 47 x 1
= 47 x ( 48 - 47 - 1 )
= 47 x 0
= 0
48x47-47x47-20-27
2256-2209-20-27
47-20-27
27-27
0