(1)拋物線y=x^2①的焦點(diǎn)F是（0,1/4）,y'=2x,
設(shè)AB:y=kx+1/4,代入①,
x^-kx-1/4=0,
設(shè)A(x1,x1^),B(x2,x2^),P(x,y),x1≠x2,則
x1+x2=k,x1x2=-1/4,
PA:y-x1^=2x1(x-x1),y=x1(2x-x1),
PB:y-x2^=2x2(x-x2).y=x2(2x-x2),
解得x=(x1+x2)/2=k/2,
y=x1x2=-1/4.
∴P點(diǎn)軌跡方程是y=-1/4.
(2)PF的斜率=（1/2）/（-k/2)=-1/k,
∴PF⊥AB.