无间qq
幼苗
共回答了13个问题采纳率:92.3% 举报
(1).y=x^2-2x-3=x^2-2x+1-1-3
=(x-1)^2-4
(2).y=2x^2-5x+7=2(x^2-2.5x+1.25^2-1.25^2)+7
=2[(x-1.25)^2-1.5625]+7
=2(x-1.25)^2-3.125+7
=2(x-1.25)^2+3.875
(3).y=3x^2+2x=3[x^2+(2/3)x+(1/3)^2-(1/3)^2]
=3[(x+1/3)^2-1/9]
=3(x+1/3)^2-1/3
(4).y=(5/2)x-2-3x^2=-3[x^2-(5/6)x+(5/12)^2-(5/12)^2]-2
=-3[(x-5/12)^2-25/144]-2
=-3(x-5/12)^2+25/48-2
=-3(x-5/12)^2-71/48
1年前
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