An equation has an equals sign ( = ). Equations assert the absolute equality of two expressions.
Well, to answer your question,
y=6/5x is a rational function not a line.
pi divided by 6 is a constant and so its first derivative is 0. And since that is also a constant, the second derivative is 0. It is not clear what f(x) = csc(x) has to do with that!
That depends on the equation.
Without an equality sign the given expression can't be considered to be an equation but if it equals 0 then using the quadratic equation formula will give its solutions.
The slope of the graph of that equation is -1.
Just swap the letter around in the formula that you are given!