Let us define revenue (R) as price (P) times quantity (Q).
Furthermore let us suppose that the price depends linearly on the quantity.
Then by the product rule we have that
$$ \frac{\%\Delta R}{\%\Delta P} = Q + P \frac{\%\Delta Q}{\%\Delta P} $$
Furthermore by the linearity we have:
$$ \frac{\%\Delta R}{\%\Delta P} = Q_0 + 2 P \frac{\%\Delta Q}{\%\Delta P} $$
According to the course on economics that I am taking, the revenue should decrease with the price in a linear demand curve if the elasticity $\frac{\%\Delta Q}{\%\Delta P}$, which is always negative, has module greater than one.
But that does not seem obvious from the equation above, what is going on?