y=ax2+bx-7
when x=1,y=1
a+b=8
y'=2ax+b
(y-1)=2a(x-1)+b
y=2ax+(b+1-2a)4x-y-(6+1-4)=4x-y-3
过点（1,1）的抛物线的切线方程4x-y-3