The correct options are
A y=4(x−1)
B y=0
The equation of tangent to y=x2, be y=mx−m24. Putting in y=−x2+4x−4, we should only get one value of x i.e. Discriminant must be zero.
∴mx−m24=−x2+4x−4
⇒x2+x(m−4)+4−m24=0
D=0
Now, (m−4)2−(16−m2)=0
⇒2m(m−4)=0⇒m=0,4
∴y=0 and y=4(x−1) are the required tangents.
Hence, (a) and (b) are correct answers.