Their slopes must be the same, but with different y-intercepts.
Here is an example: 2x + 1 and 2x + 4 are parallel lines.
The function is graphed as shown below
Part A:
We use the formula

to find the vertex of the function. A quadratic function of the form of

and equating this form to the given function

, we have

and

.
Substituting

and

into the vertex formula, we have

, as shown in the graph
This calculation means that the highest profit is achieved when the number of photo printed equals to ten photos
Part B:
We can find solution to this equation by factorising





and

, as shown in the graph
The two values means that the company makes no profit when they either produce 5 or 15 photos
Quickly using a calculator (or long division) reveals that 191/238=<span>0.8025=80.25%, which is close to 80%=4/5
Similarly, 106/160=0.6625=66.25%, which is close to 66.67%=2/3</span>
115 degrees as 70+40=115 and that is equal to ?