Straight Line and Pair of Straight Lines 1 Question 34

34. The graph of the function cosxcos(x+2)cos2(x+1) is

(1997,2M)

(a) a straight line passing through (0,sin21) with slope 2

(b) a straight line passing through (0,0)

(c) a parabola with vertex (1,sin21)

(d) a straight line passing through the point π2,sin21 and parallel to the X-axis

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Solution:

  1. Let y=cosxcos(x+2)cos2(x+1)

=cos(x+11)cos(x+1+1)cos2(x+1)=cos2(x+1)sin21cos2(x+1)y=sin21

This is a straight line which is parallel to X-axis.

It passes through (π/2,sin21).



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