Đáp án:
Giải thích các bước giải:
Bài 1
`a, ( 1/(1×3) + 1/(3×5) + 1/(5×7) + 1/(7×9) + 1/(9×11) ) . n = 10/11`
`[ 1/2 × ( 1 - 1/3 + 1/3 - 1/5 + 1/5 - 1/7 + 1/7 - 1/9 + 1/9 - 1/11 )] × n = 10/11`
`[ 1/2 × ( 1 - 1/11 )] × n = 10/11`
`[ 1/2 × 10/11 ] × n = 10/11`
`5/11 × n = 10/11`
`n = 10/11 : 5/11`
`n = 2`
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`b, n/2 + ( n + n )/3 + ( n + n + n )/4 = 23/6`
`n/2 + ( n × 2 )/3 + ( n × 3 )/4 = 23/6`
`n . ( 1/2 + 2/3 + 3/4 ) = 23/6`
`n . 23/12 = 23/6`
`n = 23/6 : 23/12`
`n = 2`
Bài 2:
`a, 1996 × 1001 - 1996`
= `1996 × ( 1001 - 1 )`
= `1996 × 1000`
= `1996000`
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`b, 3 × 45 × 12 + 9 ×53 × 4 + 36 + 36`
= `45 × 36 + 53 × 36 + 36 × 2`
= `36 × ( 45 + 53 + 2 )`
= `36 × 100`
= `3600`