JEE Main20203 Sep 2020Evening ShiftMathematicsApplication of DerivativesActual
Suppose f x is a polynomial of degree four having critical points at - 1 , 0 , 1 . If T = x ∈ R | f x = f 0 , then the sum of squares of all the elements of T is :
Options
- A4
- B6
- C2
- D8
Correct answer
A. 4
Step-by-step solution
f ' x = k . x x + 1 x - 1 = k x 3 - x Integrating both sides with respect to x , we get f x = k   x 4 4 - x 2 2 + c ⇒ f 0 = c ∵     f x = f 0 ⇒ k x 4 - 2 x 2 4 + c = c ⇒ x 2 x 2 - 2 = 0 ⇒ x = 0 ,   2 ,   - 2 ⇒ T = 0 ,   2 ,   - 2 Thus, sum of squares of all the elements of T is 0 2 + 2 2 + - 2 2 = 4 .