Question

Which of the following are identities?

***choose ALL that apply! :D

Answer 1

answer choices A,B,C,D from top to bottom :)

***my answer: A, C, and D

is that right? :)

Answer 2

cos(x+y) = cosxcosy - sinxsiny
cos(x-y) = cosxcosy + sinxsiny

what happens if add up all 2 above :)

Answer 3

like together?

Answer 4

cosxcosy - sinxsiny + cosxcosy + sinxsiny ?

Answer 5

yes, then cancel out the sinxsiny

Answer 6

so you get 2cosxcosy ?

Answer 7

which makes the answer B,C, and D? NOT A,C, and D? is that right? :)

Answer 8

you not me :)
so, A is not identity

Answer 9

yup!! kk i get it now :)

thank you!! :D

Answer 10

yes, the rest are identities

you're welcome :)

Answer 11

:) thanks again!

Answer 12

nope ;)