$\"\"$

\

The trigonometric equation is $\"\"$ .

\

$\"\"$

\

Substitute the double angle formula $\"\"$ .

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$\"\"$

\

$\"\"$

\

The general form of equation is $\"\"$ .

\

Compare the equation with general equation.

\

$\"\"$

\

Hence,

\

$\"\"$

\

Therefore ,the function has no real solution.

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$\"\"$

\

The function has no real solution.