# Tan(A+B) problem

1. Jan 31, 2010

### lemon

1. If sinA=7/25 and sinB=5/13, where A is acute and B is obtuse, find the exact value of tan(A+B)

2. Tan(A+B)=tanA+tanB/1-tanAtanB

3. TanA=7/24
TanB=5/-12
Tan(A+B)=7/24+5/-12/1-7/24x5/-12=-36/323 or -0.1 (1d.p.)

2. Jan 31, 2010

### tiny-tim

Hi lemon!

Very good , except

read the question … it asks for the exact value, which I assume means leave it as a fraction (exactly as the original data were given).

3. Jan 31, 2010

### Staff: Mentor

Re: Tan(A+B)

Removed the extra bold tags...
Please use parentheses. You have everything jammed together, so it's difficult to tell what's in the numerator and what's in the denominator. This should be written as

tan(A + B) = (tan A + tan B)/(1 - tan A * tan B)
Again, please use parentheses. It would be clearer as

tan(A + B) = (7/24 - 5/12)/(1 - (7/24)(-5/12))
Your answer of -36/323 $\approx$ -0.111455 $\approx$ -0.1 is correct.

4. Jan 31, 2010

### lemon

Re: Tan(A+B)

Understood. Thanks to you both