It has only one solution because it is a linear equation
Answer:

Step-by-step explanation:
The equation for the monthly charge has the following format

In which y(x) is the cost in function of the number of kilowatt-hours used(x), a is the price of each killowatt hour and b is the fixed(base) charge.
Base charge of $17.32 per month.
This means that 
charge of 7.32 cents per kilowatt-hour
Our answer is in dollars. Each dollar is 100 cents. So 7.32 cents is 
Write an equation for the monthly charge y in terms of x, the number of kilowatt-hours used.


Answer:
(- 1/2 , √3/2)
Step-by-step explanation:
t=20π/3
t' = 20π/3 - 6π = 2π/3 (120°) ... 2nd quadrant
If we start from (1,0) of unit circle, the coordinate of terminal point (x,y)
OF/OE = - cos 60° = x / 1 = - 1/2
FE/OE = sin 60° = y/1 = √3/2
Let's take as example a linear function of the form:
y = kx.
Where,
k is the constant of proportionality.
Therefore, the proportionality constant is the point:
(x, kx)
Generically it is always the point:
(x, k * f (x))
Where, f (x) is a function proportional to x.
answer:
The constant of proportionality is always the point (x, k * f (x)), where k is the constant of proportionality.
The answer is D because I did the math