Sum, Difference & Product Formulae

[odolwa99]

My answer is almost correct, except for the negative sign. Can anyone help?

Many thanks.

Homework Statement

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

Homework Equations

The Attempt at a Solution

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

 

[LCKurtz]

My answer is almost correct, except for the negative sign. Can anyone help?

Many thanks.

Homework Statement

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

Homework Equations

The Attempt at a Solution

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

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

 

[odolwa99]

Thank you.