Question:
The number of real solutions to the equation \(\left | sec(x)-2\right |=k\), where \(-2\pi\le x \le2\pi\)
is determined by the value of the constant k.
Find the number of real solutions for all values of k, given that \(k\epsilon R\).
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Here is my attempt:
\(\frac{1}{cos(x)}-2=\pm k\) for \(-2\pi\le x\le 2\pi\)
\(cos(x)=\frac{1}{2\pm k}\)
\(x=cos^{-1}(\frac{1}{2\pm k}) \) ( \(-2\pi\le x\le 2\pi\) )
So:
\(-2\pi\le cos^{-1}(\frac{1}{2\pm k})\le 2\pi\) implying: \(1\le\frac{1}{2\pm k}\le1\).
Therefore, \(\frac{1}{2\pm k}=1\), so \(k=\pm1\)
Now, i subsituited k=1 and k=-1 in the original equation \(\left | sec(x)-2\right |=k\) and considering the domain, \(-2\pi\le x \le2\pi\)
found the solutions seperately for each case (I.e. k=1 and k=-1) Then counted them and they are 7 distinct solutions.
Is this correct? As I do not have a model answer to check.
Thanks in advance.
I just found a solution, what I did above is not correct.
-->Sketch the graph of \(y=\left |sec(x)-2 \right |\), and then consider y=k as k varies over R.
That is,
if k<0 -->No real solutions
if k=0 -->4 real solutions
if 0 8 real solutions
if k=1 -->7 real solutions
if 1 4 real solutions
if k=3 -->6 real solutions
if k>3 ---> 8 real solutions.