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

Toán Lớp 7: CHỨNG MINH: a,3^15+27^4 chia hết cho 28 b, 2^300<3^200

Toán Lớp 7: CHỨNG MINH:
a,3^15+27^4 chia hết cho 28
b, 2^300<3^200

Comments ( 2 )

  1. Ta có:
    3^15+27^4
    =3^15+(3^3)^4
    =3^15+3^12
    =3^12.(1+3^3)
    =3^12 . (1+27)
    =3^12 .28
    Vì 28 vdots 28=>3^12 .28 vdots 28=>3^15 + 3^12 vdots 28
    b)2^300=(2^3)^100=8^100
    3^200=(3^2)^100=9^100
    Vì 8<9=>8^100 < 9^100=>2^200<3^300

  2. a) 3^15 + 27^4
    = 3^15 + (3^3)^4
    = 3^15 + 3^12
    = 3^12 ( 3^3 + 1 )
    = 3^12 . 28
    Nên 3^12 . 28 chia hết cho 28
    b) 2^300 = (2^3)^100 = 8^100
    3^200 = (3^2)^100 = 9^100
    Vì 8 < 9 nên 8^100 < 9^100
    Do đó 2^300 < 3^200
    CHÚC HỌC TỐT

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

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