The cost of a telephone call is $0.75 + $0.25 times the number if minutes. write an algebraic expression that models the cost of a telephone call that lasts t minutes

The cost of $0.75 is fixed, so the total cost of the phone call can't be less than 0.75.

Then, we add the variable part, the one depending on the number of minutes. If every minutes costs $0.25, then minutes cost dollars.

So, if you add the fixed and variable prices, you have the function modelling the cost of a telephone call that lasts minutes:

if the eqn of the parabola is f(x) = (x-4)(x+2), we need to mult. this out to find the coordinates of the vertex.

then f(x) = x^2 + 2x - 4x - 8, and f(x) = x^2 - 2x - 8.

one way in which you can find the vertex is to calculate x = -b / (2a).   here, that comes to

        )

x = = 1.   f(1) = 1^2 - 2(1) - 8 = - 9.   vertex is at (1, -9).

        2(1) 

find another point on the curve:   let x=0, for which y=-8.   then (0, -8) is on the curve.   plot the vertex and this point and draw a smooth parabola thru both.

hope this