Question

I REAAAAAALLLLLLY NEED HELP! :'(
express cos80ºcos70º+sin80ºsin70º as a single trigonometric function of a positive acute angle.

Answer 1

well the answer is;0.86255518

Answer 2

how did you get that?

Answer 3

you need to use the double angle formula for cosine:
\[\cos(\theta-\phi)=\cos(\theta)\cos(\phi)-\sin(\theta)\sin(\phi)\]

Answer 4

You have \[\theta = 80, \phi = 70\]

Answer 5

Correction - the sign on the right-hand side should be +, not -.

Answer 6

your late dude

Answer 7

Not really - he asked for an explanation.

Answer 8

but cool cause my friend needed the formula thanks

Answer 9

or she...