First slide
Functions (XII)
Question

Let f(x)=sin23xcos22x and g(x)=1+12tan1|x|. Then the number of values of x in the interval [10π, 8π] satisfying the equation f(x)=sgn(g(x)) is _____.

Moderate
Solution

g(x)=12tan1|x|+1

 or     sgn(g(x))=1 or     sin23xcos22x=1

 or    sin23x=1+cos22x

which is possible if sin x = 1 and cos x = 0. Therefore,

sinx=1,x=2+π2

Hence, 10π2+π28π   or   214n154

 or  5n3

Hence, number of values of x = 9.

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