推 feynmax:感謝大大 04/06 23:08
※ 引述《feynmax (max)》之銘言：
: x^2+bx+3b
: lim ---------- = 8
: x→a x-a
: then (a,b)=?
: 請問各位板大，這一題該如何解答呢?
為0/0不定型極限 => a^2+ab+3b=0 ---(i)
由L'Hospital's Rule
x^2+bx+3b 2x+b
lim ---------- = lim ------ =2a+b=8 ---(ii)
x->a x-a x->a 1
(i)(ii)解聯立得 (a,b) = (6,-4) or (-4,16)
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