Here is a slightly tough question in CAT 2019. It combines the topics of trigonometry and algebra. It is very important to have done a solid CAT Preparation to be sure about the concepts and trigonometry formula to even attempt this question. Once you are clear with the concepts & formulas, it would be prudent to practice them from CAT previous year paper.
Question 17 : The number of the real roots of the equation 2cos(x(x + 1)) = 2x + 2-x is
2cos (x(x + 1)) = 2x + 2-x
Consider RHS, 2x + 2-x
This is of the form,
We know that when y is positive and when y is negative
Here, since we are dealing with 2x, is considered
So, 2cos (x (x + 1))
Substitute x = 0, 2x + 2-x = 20 + 20 = 2
2cos (x (x + 1)) = 2cos (0(0 + 1)) = 2cos (0) = 2 x = 0 is a valid solution
Any value other than this wont work.
Therefore, only x = 0 works and there is only one real solution
The question is "The number of the real roots of the equation 2cos(x(x + 1)) = 2x + 2-x is "
Choice C is the correct answer.
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