Question 1189292
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<pre>

It is a linear equation if and only if f(x) is a linear function of x of the form 

    f(x) = ax + b.



If, on contrary, f(x) is not a linear function, then equation  f(x) = -5  is not linear.
</pre>

Thoroughly answered and explained.



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Ignore the post by @josgarithmetic as non-sensical.