Finding the range of \(\displaystyle{f{{\left({x}\right)}}}={\cos{{x}}}{\left({\sin{{x}}}+\sqrt{{{\frac{{12}}{+}}{{\sin}^{{2}}{x}}}}\right)}\)

Jefferson Pacheco

Jefferson Pacheco

Answered question

2022-04-08

Finding the range of f(x)=cosx(sinx+12+sin2x)

Answer & Explanation

Ferrito90gn

Ferrito90gn

Beginner2022-04-09Added 12 answers

hint: Put u=cosx,v=sinx, then the problem becomes: Find the min/max of the function f(u,v)=u(v+12+v2), subject to u2+v2=1 by Lagrange Multiplier method. I think it is doable this way. Can you try ? It is two variable function but it is much nicer than the original function indeed !
chambasos6

chambasos6

Beginner2022-04-10Added 12 answers

Done it!
Let f(x)=y
ysecx-sinx=sin2x+12
y2sec2x2ysecxsinx=122y2(tan2x)+4ytanx+2y21=0
For tanx to be real, Δ0
6y2-4y40-32y32
Which is the correct range according to the graph as well.
Hence, the number of integers in the range of f(x) is 3: 0,-1 and 1

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