Math Is Fun Forum

Trigtrigger

Guest

Exponential problem

Can anyone assist with the following problem to find a where x = 0.85, k=1 and y = 11.2;

y=ae^-k*x

Thank you

Bob

Administrator

Registered: 2010-06-20

Posts: 10,640

Re: Exponential problem

hi Trigtrigger

Welcome to the forum.

Can anyone assist with the following problem to find a where x = 0.85, k=1 and y = 11.2;

y=ae^-k*x

Please see next post by Alg Num Theory.  I'll leave mine as a testament to the importance of 'reading the question' !!!

So 11.2 = a^(-0.85)

If you take logs (any will do but let's use base 10 as it's handy on a calculator) you get

log(11.2) = log(a^-0.85) = -0.85 * log(a)

So re-arrange this to make log(a) the subject, and inverse log it (ie. raise 10 to the power of) and you'll get a.

eg.  If log(a) = 2 then a = 10^2 = 100

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

Alg Num Theory

Member

Registered: 2017-11-24

Posts: 693

Website

Re: Exponential problem

Can anyone assist with the following problem to find a where x = 0.85, k=1 and y = 11.2;

y=ae^-k*x

So 11.2 = a^(-0.85)

Last edited by Alg Num Theory (2018-01-12 16:14:28)

---

Me, or the ugly man, whatever (3,3,6)

Bob

Administrator

Registered: 2010-06-20

Posts: 10,640

Re: Exponential problem

Thanks Alg Num Theory.  I seem to have lost an 'e'.  Thanks for the correction.  I have edited my post as a penance.

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob