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

Toán Lớp 6: tính A = 1.2 + 2.3 + 3.4 + 4.5 + 5.6 + –… + 30.31

Toán Lớp 6: tính A = 1.2 + 2.3 + 3.4 + 4.5 + 5.6 + ……….. + 30.31

Comments ( 1 )

  1. Giải đáp+Lời giải và giải thích chi tiết:
     A=1.2+2.3+3.4+4.5+5.6+….+30.31
    3A=1.2.3+2.3.3+3.4.3+4.5.3+5.6.3+…+30.31.3
    3A=1.2.3+2.3.(4-1)+3.4.(5-2)+4.5.(6-3)+5.6.(7-4)+….+30.31.(32-29)
    3A=1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+4.5.6-3.4.5+5.6.7-4.5.6+…+30.31.32-29.30.31
    3A=(1.2.3-1.2.3)+(2.3.4-2.3.4)+(3.4.5-3.4.5)+(4.5.6-4.5.6)+….+30.31.32
    3A=30.31.32
    A=(30.31.32)/3
    A=10.31.32
    A=9920
    Vậy A=9920

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