Question

Medal and fan for those who can help me with precalc :)

Answer 1

@Nurali

Answer 2

@mathmate its a tough problem mate :/ could you please help

Answer 3

Hint:
Use FOIL to get the products
then use trigo identities to simplify:
cos(a+b)=cos(a)cos(b)-sin(a)sin(b)
sin(a+b)=sin(a)cos(b)+cos(a)sin(b)

Answer 4

do you multiply 3*7 by any chance?

Answer 5

Im leaning towards A

Answer 6

@mathmate @Nurali

Answer 7

7 and 3 are multiplied similar to
3(x+1) * 7(x-1) = 21(x^2-1)

Answer 8

never mind i got it its c

Answer 9

I was doing it wrong

Answer 10

bonne chance!

Answer 11

3/7 (cos (-pi/8)

Answer 12

Merci

Answer 13

c'est vrai @mathmate ?