Results 1 to 2 of 2

Thread: Calculate!

  1. #1
    Super Member
    Joined
    Dec 2009
    Posts
    755

    Calculate!

    Given that $\displaystyle \frac{cos(A-B)}{cos(A+B)}=\frac{7}{5}$, prove that $\displaystyle cosAcosB = 6sinAsinB$ and deduce a relationship between $\displaystyle tanA$ and $\displaystyle tanB$. Given further that $\displaystyle A+B=45^\circ$, calculate the value of $\displaystyle tanA+tanB$.

    I have already proved the equation.

    I have also tried to deduce the relationship between tanA and tanB,

    $\displaystyle cosAcosB=6sinAsinB$

    $\displaystyle \frac{cosAcosB}{sinAsinB}=\frac{1}{6}$

    [Math]tanAtanB=\frac{1}{6}[/tex]

    But am not sure if I am on the right track. Lastly, need help with calculating the value of $\displaystyle tanA+tanB$
    Last edited by Punch; Jan 22nd 2010 at 01:40 AM.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Opalg's Avatar
    Joined
    Aug 2007
    From
    Leeds, UK
    Posts
    4,041
    Thanks
    10
    Yes, you are on the right track (except that the 6 should be 1/6 — remember that tan = sin/cos, not cos/sin). For the last part, use the formula $\displaystyle \tan(A+B) = \frac{\tan A + \tan B}{1-\tan A\tan B}$.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Is it possible to calculate x and y....
    Posted in the Algebra Forum
    Replies: 2
    Last Post: Nov 29th 2010, 01:16 PM
  2. calculate
    Posted in the Algebra Forum
    Replies: 5
    Last Post: Apr 27th 2010, 09:35 AM
  3. Calculate
    Posted in the Calculus Forum
    Replies: 1
    Last Post: Apr 14th 2010, 02:11 AM
  4. Calculate M4
    Posted in the Calculus Forum
    Replies: 5
    Last Post: Mar 29th 2010, 08:44 PM
  5. Calculate this sum
    Posted in the Number Theory Forum
    Replies: 1
    Last Post: Aug 28th 2009, 11:50 PM

Search Tags


/mathhelpforum @mathhelpforum