Theory of Equations 5 Question 4

4. The real number k for which the equation, 2x3+3x+k=0 has two distinct real roots in [0,1]

(2013 Main)

(a) lies between 1 and 2

(b) lies between 2 and 3

(c) lies between -1 and 0

(d) does not exist

Show Answer

Solution:

  1. Let f(x)=2x3+3x+k

On differentiating w.r.t. x, we get

f(x)=6x2+3>0,xR

f(x) is strictly increasing function.

f(x)=0 has only one real root, so two roots are not possible.



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