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Simple exponential expand

Posted 2 days ago

Is there a way to expand an exponential of a sum to a product of exponentials? Example:

Exp[a+b]

I want Mathematica to expand it to Exp[a]*Exp[b]. In my example, the full expression is Exp[a+b]+c*Exp[a+d] and I want to factor with respect to Exp[a] and expand to trig the terms Exp[b] and Exp[d], where b and d are imaginary numbers.

Thanks!

POSTED BY: Harris Lyr
3 Replies

Just one variation:

Exp[a + b] + c Exp[a + d] /. a -> Log[Defer[E^a]]
POSTED BY: Gianluca Gorni
Posted 1 day ago

Yes, in Mathematica, you can expand an exponential of a sum using the rule: exp(a+b)=exp(a)⋅exp(b)

For your specific expression Exp[a + b] + c Exp[a + d], you can factor Exp[a] and express it in terms of exponentials of b and d, especially if they are imaginary numbers.

Mathematica Code: mathematica

Exp[a + b] + c Exp[a + d] // Expand (* Output: Exp[a] Exp[b] + c Exp[a] Exp[d] *)

Factor[Exp[a + b] + c Exp[a + d], Exp[a]] (* Output: Exp[a] (Exp[b] + c Exp[d]) *) If b and d are purely imaginary, you can further use trigonometric expansion:

mathematica

ExpToTrig[Exp[I b] + c Exp[I d]] This will convert exponentials of imaginary numbers into sine and cosine terms.

Summary: Use Expand to apply Exp[a + b] → Exp[a] Exp[b]. Use Factor to extract common terms like Exp[a]. Use ExpToTrig to convert exponentials of imaginary numbers into trigonometric functions.

POSTED BY: Asad Hasnain

Since Exp[a] Exp[b] automatically evaluates to Power[E, Plus[a, b]], it's impossible to keep Exp[a] Exp[b] as is, unless you use Hold[] or HoldForm[].

On the other hand, we have this:

Factor[Exp[a + b] + c Exp[a + d]]
(*  E^a (E^b + c E^d)  *)

If a, b, c, d have numeric values, then you have to take a more manual approach, since the numbers will combine with one another. Try the following:

Exp[a] Expand[(Exp[a + b] + c Exp[a + d])/Exp[a]]
POSTED BY: Michael Rogers
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