Quick Help with Tangent Sum Formula: Solving for Tan 15 and Tan 30

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The discussion revolves around a pre-calculus problem involving the tangent sum formula, specifically calculating Tan(15) + Tan(30) using the formula Tan(a+b) = (Tan a + Tan b) / (1 - Tan a * Tan b). The correct calculation leads to Tan(45), which equals 1, contradicting the initial claim of the answer being -1. Participants clarify that the book likely contains a misprint, as the application of the formula confirms the correct result. The conversation highlights the importance of correctly applying trigonometric identities in solving tangent problems. Understanding these formulas is crucial for accurate calculations in pre-calculus.
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Hi, I'm studying for my pre-calc test tomorrow and I've run into a snag. I just can't seem to get the correct answer for a Tangent sum problem, and I'm hoping someone could help me out with it. It goes like this:

Sum Formula for Tangant: Tan (a+b) = Tan a + Tan b/1-Tan a * Tan b

Problem: Find the exact value,
Tan 15 + Tan 30/1- Tan 15 * Tan 30

Correct answer: -1

but I can't seem to get the answer in the end; are the tangants in the numerator added to make tan 45 then solved for? If not, how would you express tan 15 in an exact form? Similarly, how do you multiply tan 15 and tan 30? Or am I missing some other identity?

Its been driving me crazy all day!:cry:
 
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(Tan 15 + Tan 30) / (1- Tan 15 * Tan 30) =
Tan(15+30) =
Tan(45) =
1

The answer you have is wrong.
 
I don't think that's the correct answer. It should be 1. Just apply the formula backwards to get it.
 
Huh, that's quite odd... misprint in the book I suppose. Heh, it makes more sense now, thanks!
 

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