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

Toán Lớp 7: Chứng tỏ : a) x mũ 2 – 6x + 15 > 0 với mọi x

Toán Lớp 7: Chứng tỏ :
a) x mũ 2 – 6x + 15 > 0 với mọi x

Comments ( 2 )

  1. a) Có : x^2 -6x +15
    =x^2 -2.3x + 9 +6
    =x^2 -2.3x +3^2 +6
    =(x-3)^2 +6
    Vì (x-3)^2 >=0 mọi x 
    Suy ra : (x-3)^2 +6 >0 mọi x
    Vậy x^2 -6x +15 >0 mọi x (đpcm)
     

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