Question

2,3问急求过程，非常感谢

Answer 1

(1)易知A(0，4),由4=ax^2-3ax+4得B(3，4),
BC:y=kx-4k+2,
∴4=-k+2,k=-2.
∴BC:y=-2x+10,交x轴于C(5，0),
抛物线过点C,
∴0=25a-15a+4,a=-0.4,
∴抛物线y=-0.4x^2+1.2x+4与x轴交于D(-2，0).AD=2√5.
(2)E(t,0),0<t<5,DE=2+t,
易知△EDF∽△ADO,
∴DF/DO=DE/AD,
DF=DE*DO/AD=(2+t)/√5，
FH∥AO,
∴FH/AO=DF/DA，
d/4=(2+t)/10,d=2t/5+4/5.
(3)DH/DO=FH/AO,DH=t/5+2/5,F(t/5-8/5,2t/5+4/5).
P(t,-0.4t^2+1.2t+4),
△PEF是以PF为腰的等腰三角形：
1)PF=EF,d=yP/2,2t/5+4/5=-0.2t^2+0.6t+2,
t^2-t-6=0,t=3.
2)PF=PE,(4t/5+8/5)^2+(0.4t^2-0.8t-3.2)^2=(-0.4t^2+1.2t+4)^2,
(0.8t+1.6)^2=(0.4t+0.8)(-0.8t^2+2t+7.2),0.4t+0.8>0,
∴1.6t+3.2=-0.8t^2+2t+7.2,
0.8t^2-0.4t-4=0,
2t^2-t-10=0,t=2.5.

Answer 2

发个清楚的图

追答

尤其是抛物线