find the rate, solve for r

I ussually dont need help for the types of question, but I am having alot of diffuculty isolating r by itself on one side of the = sign.

Assume a person invests $210 at the end of each year for 10 years at an annual interest rate of r. The ammount of money, A, in the account after 10 years is

A =

his goal is to have 3089 in his account after 10 years.

Re: find the rate, solve for r

Quote:

Originally Posted by

**delgeezee** I ussually dont need help for the types of question, but I am having alot of diffuculty isolating r by itself on one side of the = sign.

Assume a person invests $210 at the end of each year for 10 years at an annual interest rate of r. The ammount of money, A, in the account after 10 years is

A =

his goal is to have 3089 in his account after 10 years.

This is an equation of 9th degree in r. I doubt that you'll find a solution in closed form.

Re-arrange the equation to

and use (for instance) Newton's method to get an approximate value of r.

I've got