1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Sum, Difference & Product Formulae

  1. Nov 8, 2012 #1
    My answer is almost correct, except for the negative sign. Can anyone help?

    Many thanks.

    1. The problem statement, all variables and given/known data

    Q. Without using a calculator, show that [itex]\sin10^{\circ}+\sin80^{\circ}=\sqrt{2}\cos35^o[/itex]

    2. Relevant equations

    3. The attempt at a solution

    [itex]2\sin(\frac{90}{2})\cos(\frac{-70}{2})[/itex]
    [itex]-2\sin45\cos35[/itex]
    [itex]-2(\frac{1}{\sqrt{2}})\cos35[/itex]
    [itex]\frac{-2}{\sqrt{2}}\cos35[/itex]
    [itex]\frac{-2\sqrt{2}}{2}\cos35[/itex]
    [itex]-\sqrt{2}\cos35[/itex]
     
  2. jcsd
  3. Nov 8, 2012 #2

    LCKurtz

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    ##\cos(-35)=+\cos(35)##
     
  4. Nov 8, 2012 #3
    Thank you.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Sum, Difference & Product Formulae
Loading...