Math Is Fun Forum

Daniel123

Member

Registered: 2007-05-23

Posts: 663

Am I being stupid

How would you solve e^x = x² - 1?

EDIT: This is the 7777th topic

Last edited by Daniel123 (2008-02-16 11:54:14)

JaneFairfax

Member

Registered: 2007-02-23

Posts: 6,868

Re: Am I being stupid

Plotting the graphs shows that there is a solution in x between −2 and −1. Otherwise I don’t think there is any way of expressing the solution in “closed” form.

EDIT: This is the 7777th topic

At the moment, the topic 0.9999....(recurring) = 1? has 911 replies.

Daniel123

Member

Registered: 2007-05-23

Posts: 663

Re: Am I being stupid

Ahh good. I was getting myself confused.. I'm not having a good maths day.

EDIT: THANKS. I really am tired.. forgetting my manners.

Last edited by Daniel123 (2008-02-16 12:14:53)

Daniel123

Member

Registered: 2007-05-23

Posts: 663

Re: Am I being stupid

At the moment, the topic 0.9999....(recurring) = 1? has 911 replies.

And the two topics below have 9 then 11 replies.

Last edited by Daniel123 (2008-02-16 12:20:17)

mathsyperson

Moderator

Registered: 2005-06-22

Posts: 4,900

Re: Am I being stupid

You can get it to as many decimal places as are on your calculator by putting -1.5 = (or some number close to that), and then putting -√(eAns+1) and pressing = lots of times.

As for an exact analytic answer, I don't see a way of getting one either.

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Why did the vector cross the road?
It wanted to be normal.

MathsIsFun

Administrator

Registered: 2005-01-21

Posts: 7,711

Re: Am I being stupid

The graph: Plot of e^x vs x^2-1 they cross over around -1.1477576

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"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman