Straight Line Question 67

Question: The graph of the function $ \cos x\ \cos (x+2)-{{\cos }^{2}}(x+1) $ is [IIT 1997 Re-Exam]

Options:

A)A straight line passing through $ (0,-{{\sin }^{2}}1) $ with slope 2

B)A straight line passing through (0, 0)

C)A parabola with vertex $ 75^{o} $

D)A straight line passing through the point $ ( \frac{\pi }{2},-{{\sin }^{2}}1 ) $ and parallel to the x?axis

Show Answer

Answer:

Correct Answer: D

Solution:

  • $ y=\cos (x+1-1)\cos (x+1+1)-{{\cos }^{2}}(x+1) $ $ ={{\cos }^{2}}(x+1)-{{\sin }^{2}}1-{{\cos }^{2}}(x+1)=-{{\sin }^{2}}1 $ , which represents a straight line parallel to x-axis with $ y=-{{\sin }^{2}}1 $ for all x and so also for $ x=\pi /2 $ .