Toán Lớp 8: A=-2x^2+6x+9
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Toán Lớp 8: A=-2x^2+6x+9
tìm x
Cảm ơn nhìu
Comments ( 2 )
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A=-2x^2+6x+9
=-2(x^2-3x-9/2)
=-2[x^2-2*x*3+(3/2)^2-27/4]
=-2(x-3/2)^2+27/2 le 27/2 ∀x (x\inRR)
Dấu “=” xảy ra khi :
x-3/2=0
<=>x=3/2
Vậy A_{max}=27/2 khi và chỉ khi x=3/2