The transformations that can occur to the graph of the function y = cos x that will exhibit changes would be changes to the angle, or changes to the coefficient. The transformations can be viewed as follows:
y = cos x transforms to y = cos (kx)
k > 1 ; a horizontal shrink occurs
0 < k < 1 ; a horizontal stretch occurs
y = cos x transforms to y = A cos x
|A| > 1 ; a vertical stretch occurs
|A| < 1 ; a vertical shrink occurs
Given:
The power generated by an electrical circuit (in watts) as function of its current x (in amperes) is modeled by:

To find:
The current that will produce the maximum power.
Solution:
We have,

Here, leading coefficient is negative. So, it is a downward parabola.
Vertex of a downward parabola is the point of maxima.
If a parabola is
, then

In the given function, a=-12 and b=120. So,



Putting x=5 in the given function, we get




Therefore, 5 watt current will produce the maximum power of 300 amperes.
Yes it proportional because they all function of y=3x
0x3=0
2x3=6
4x3=12
6x3=18