JEE Advanced2006MathematicsParabolaActual
Equation of common tangent of y=x^2, y=-x^2+4 x-4 is
Options
- Ay=4(x-1)
- By=0
- Cy=-4(x-1)
- Dy=-30 x-50
Correct answer
A. y=4(x-1)
Step-by-step solution
The equation of tangent to y=x^2 , be y=m x- m^2 4 , putting in y=-x^2+4 x-4 , we should only get one value of x i.e. Discriminate must be zero. array rrr & m x- m^2 4 & =-x^2+4 x-4 & x^2+x(m-4)+4- m^2 4 & =0 & m(m-4) & =0 & y=0 & or m=0,4 array y=0 and y=4(x-1) are tangents.