- 在直线X
- 急用,在线。
- P (a , a-2)
AP斜率K1=[1-(a-2)]/(-1-a ) =(a-3)/(a+1)
BP斜率K2=[1 -(a-2)]/(1-a) = (a-3)/(a-1)
所夹的角为b
tanb =U=(K2-K1)/(1+K2K1)
===> U= (2a-6)/(2a^2-6a+8)
= (a-3)/(a^2 -3a+4)
==> Ua^2 -(3U+1)a+4U+3 =0
△ = -7U^2 -6U+1≥0
==>U∈[-1 , -1/7]
tanb =-1 ==>夹角b =3∏/4最大
(a-3)/(a^2 -3a+4) =-1 ==>a =1
P (1 ,-1)