f(x)=ax^2+bx
f(2)=4a+2b=0
f(x)=ax^2+bx=x
ax^2+bx-x=0
ax^2+x(b-1)=0(且方程f(x)=x有等根)
△=0.(b-1)^2=0.b=1
4a+2b=0.a=-1/2
f(x)的解析式f(x)=-1/2x^2+x
f(x)=ax^2+bx
f(2)=4a+2b=0
f(x)=ax^2+bx=x
ax^2+bx-x=0
ax^2+x(b-1)=0(且方程f(x)=x有等根)
△=0.(b-1)^2=0.b=1
4a+2b=0.a=-1/2
f(x)的解析式f(x)=-1/2x^2+x