Question

evaluate cos 220 cos40+sin220sin40

Answer 1

This question came up earlier, I think spanishkb31 is in your class...

Answer 2

okay, cos(-40) = cos(40)
and cos(a+b) = cos(a)cos(b) - sin(a)sin(b)...

Answer 3

Nice memory :o

Answer 4

so what is (a+b)?

Answer 5

you there?

Answer 6

yea

Answer 7

yea

Answer 8

you all set?

Answer 9

no lost

Answer 10

whats the step

Answer 11

well, if you replace cos(40) with cos(-40), you get:
cos 220 cos(-40) - sin220sin(-40)
which is the sum of angles formula for cosine
cos(a+b) = cosa cosb - sina sinb
so, what is (a+b) ?

Answer 12

im confused

Answer 13

whats the answer