Find, using calculus, the x coordinate of the turning point of the curve with equation y=e^3x cos 4

1st step: find the derivative dy/dx of the given equation2nd step: now equate the obtained derivative to 0 because this is precisely the situation in which the graph changes direction (the derivative dy/dx equated to 0 means that the gradient m at that point equals 0. which if you think of logically makes sense to be the gradient at which the direction of the graph changes)3rd step: now just find the value of x from the obtained equation. The value of x you find corresponds to the x-cordinate of the turning point