Use the model =APert or =AP+1rnnt, where A is the future value of P dollars invested at interest rate r compounded continuously or n times per year for t years. If $15,000 is invested in an account earning 7.5% interest compounded continuously, determine how long it will take the money to double. Round up to the nearest year.

ANSWER

EXPLANATION

We want to write the equation of a parabola with vertex (-5,8) and directrix x=2.

The equation of the directrix tells us that, the axis of symmetry of the parabola is parallel to the x-axis.

This type of parabola has equation of the form:

p is the focal length of the parabola.

p=-7 because the parabola opens along the negative x-axis.

Hence the equation is