※ 引述《cklevel1 (小舜)》之銘言：
: https://i.imgur.com/swV17t5.png
: 請問為何
: g(h,k)=1/2(2ah+bk+d)+1/2(bh+2ch+e)+1/2(dh+ek+2f)?
g(h, k) = f'
= ah^2 + bhk + ck^2 + dh + ek + f
= (1/2)[2ahh + 2bhk + 2ck^2 + 2dh + 2ek + 2f]
= (1/2)[h(2ah + bk + d) + k(bh + 2ck + e) + (dh + ek + 2f)]
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