MHT CET202121 Sep 2021Evening ShiftMathematicsApplication of DerivativesActual

The abscissa of the points, where the tangent to the curve y=x^3-3 x^2-9 x+5 is parallel to X -axis are

Options

Ax=1 and -1
Bx=1 and -3
Cx=-1 and 3
Dx=0 and 1

Correct answer

C. x=-1 and 3

Step-by-step solution

We have y=x^3-3 x^2-9 x+5 d y d x =3 x^2-6 x-9 and since tangent is parallel to X axis, we write aligned & 3 x^2-6 x-9=0 x^2-2 x-3=0 i.e. (x-3)(x+1)=0 & x=-1,3 aligned

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