Question

已知点(-4,4),B(1,1),点C在Y轴上,若∠ACB=90°,求点C的坐标

Answer 1

设C(0,y)

若∠ACB=90°,kAC*kBC=-1

kAC=(y-4)/4

kBC=(y-1)/(-1)

kAC*kBC=(y-4)(y-1)/(-4)=-1

y^2-5y+4=4 y^2-5y=0

y=0或y=5

点C的坐标(0,0)或(0,5)