Another inverse problem!

sonya

i keep getting stuck on these inverse problems...

the question is

let f(x)=5+2x+5e^x
f^-1(10)=?

i keep messing up on these problems and now im not really sure where exactly 2 start...i know i gotta find the inverse but i would appreciate some help on getting started on this problem.....thx

Related Introductory Physics Homework Help News on Phys.org

HallsofIvy

Homework Helper
There is no way to algebraically find the inverse function to f(x)- not with x both in the exponent and as a base.

However, the problem does NOT ask you to find "f-1", it only asks you to find "f-1(10)".

Can you think of a value of x such that f(x)= 10 and what does that have to do with the problem?

sonya

well....f(x)=10 when x=0
but i dont c ne relation btwn that and the inverse...

HallsofIvy

Homework Helper
Then I think we've discovered WHY you keep "getting stuck on these inverse problems"!! That's the DEFINITION of inverse!

Two functions (call them f and g) are "inverse" to each other (here's the "formal" definition) if and only if f(g(x))= x and g(f(x))= x for all x.

If f(x)= y, then f-1(f(x))= f-1(y)= x.

Since f(0)= 10, f-1(10)= 0.

Whenever f(a)= b, then f-1(b)= a.

if f: x-> y then f-1y-> x

sonya

thats it?....how come it looks so simple now?....neways thx 4 clearing things up!...

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving