# Homework Help: Sum, Difference & Product Formulae

1. Nov 8, 2012

### odolwa99

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 $\sin10^{\circ}+\sin80^{\circ}=\sqrt{2}\cos35^o$

2. Relevant equations

3. The attempt at a solution

$2\sin(\frac{90}{2})\cos(\frac{-70}{2})$
$-2\sin45\cos35$
$-2(\frac{1}{\sqrt{2}})\cos35$
$\frac{-2}{\sqrt{2}}\cos35$
$\frac{-2\sqrt{2}}{2}\cos35$
$-\sqrt{2}\cos35$

2. Nov 8, 2012

### LCKurtz

$\cos(-35)=+\cos(35)$

3. Nov 8, 2012

Thank you.