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222-9+11+12:2*14+14 = ? ( )

Toán Lớp 7: D=5/( 7.9.11) + 5/9.11.13 +…+ 5/59.61.63 E= 4/(5.8.11 ) + 4/8.11.14 +…+4/17.20.23 Làm ơn giúp em với ạ, em đang học nên cần gấp

Toán Lớp 7: D=5/( 7.9.11) + 5/9.11.13 +…+ 5/59.61.63
E= 4/(5.8.11 ) + 4/8.11.14 +…+4/17.20.23
Làm ơn giúp em với ạ, em đang học nên cần gấp

Comments ( 1 )

  1. Giải đáp:
    D=5/(7.9.11)+5/(9.11.13)+…+5/(59.61.63
    =>D/5=1/(7.9.11)+1/(9.11.13)+…+1/(59.61.63
    =>(4D)/5=4/(7.9.11)+4/(9.11.13)+…+4/(59.61.63
    =>(4D)/5=(11-7)/(7.9.11)+(13-9)/(9.11.13)+…+(63-59)/(59.61.63
    =>(4D)/5=1/7.9-1/9.11+1/9.11-1/11.13+…+1/59.61-1/61.63
    =>(4D)/5=1/7.9-1/61.63
    =>(4D)/5=1/63-1/3843
    =>(4D)/5=20/1281
    =>4D=20/1281*5
    =>4D=100/1281
    =>D=100/1281:4
    =>D=25/1281
    E= 4/(5.8.11 ) + 4/(8.11.14) +…+4/(17.20.23
    =>E/4=1/(5.8.11 ) + 1/(8.11.14) +…+1/(17.20.23
    =>(6E)/4=6/(5.8.11 ) + 6/(8.11.14) +…+6/(17.20.23
    =>(6E)/4=(11-5)/(5.8.11 ) + (14-8)/(8.11.14) +…+(23-17)/(17.20.23
    =>(6E)/4=1/5.8+1/8.11+1/8.11-1/11.14+…+1/17.20-1/20.23
    =>(6E)/4=1/5.8-1/20.23
    =>(6E)/4=1/40-1/460
    =>(6E)/4=21/920
    =>6E=21/920*4
    =>6E=21/230
    =>E=21/230:6
    =>E=21/1380

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222-9+11+12:2*14+14 = ? ( )

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