[求助] 一元二次

原帖由 sapphire 於 11/9/2007 07:24 PM 發表

                               
登錄/註冊後可看大圖

hv u learn the eqt. D=b^2-4ac yet? in fact this question is extremely easy after u learn this.

2x^2+2p=(4p+1)x
2x^2-(4p+1)x+2p=0  which is a quad. eqt. in x

the eqt. has equal real root if and  ...

原帖由 水龍蜥 於 11/9/2007 08:48 PM 發表

                               
登錄/註冊後可看大圖

忘記了用交叉法..難怪計不到

原帖由 ccshong28 於 11/9/2007 09:38 PM 發表

                               
登錄/註冊後可看大圖

我係F.2既，想問下咩係交叉法= ='
我係咁諗既：
2x^2+2p=(4p+1)x
2x^2=4px+x-2p
2x^2-x=4px-2p
x(2x-1)=2p(2x-1)
x=2p

When x=2p,
2x^2+2p=(4p+1)x
2(2p)^2+2p=(4p+1)x
4p^2+4p^2+2p=(4p+1)x
4p^2+4 ...

2x^2-x=4px-2p
x(2x-1)=2p(2x-1)
x=2p

原帖由 sapphire 於 11/9/2007 10:24 PM 發表

                               
登錄/註冊後可看大圖

apart from the reply above

here u should not divide both sides by (2x-1)
always remember that u should not divide both sides by a number with an unknown as the number divided may equal to zero