Question

write the product as a sum
7cos6xcos7x

Answer 1

first, 7cos6xcos7x = 7/2 * (2cos6xcos7x)
to simplify that in bracket, use the formula :
2cosAcosB = cos(A+B) + cos(A-B)

Answer 2

how do you know what a and b equal?\

Answer 3

let A=6x and B=7x

Answer 4

so i got cos(6x+7x)+cos(6x-7x)

Answer 5

Can you use the the Cosine Sum/Difference identity? \[\cos(a + b) = \cos a \cos b - \sin a \sin b\]I'll give you a hint. First multiply both sides by 7. Then if we let a = 6x and b = 7x, how could you re-arrange the identity to solve just for 7cos(6x)cos(7x)?

@NorthGeorgiaBoy17

Answer 6

dont forget about 7/2 infront ...

Answer 7

I'm using a different identity.

Answer 8

us should use 2 formulas to get a new formula :)
cos(a+b)=cosacosb−sinasinb
cos(a-b)=cosacosb+sinasinb
--------------------------- +
cos(a+b) + cos(a-b) = 2cosacosb
@genius12

Answer 9

hehehe =)

Answer 10

:)

Answer 11

btw, i have to go now....

Answer 12

byebye.

Answer 13

okay so i plugged 6x for A and 7x for B. Do i just simplify it out or do i leave it??

Answer 14

bye ^ (infinity) :)

Answer 15

lol =)

Answer 16

@NorthGeorgiaBoy17

Like @RadEn mentioned, factor out 7/2. Then change 2cos(7x)cos(6x) and write it as a sum using the identity:

2cosAcosB = cos(A + B) + cos(A - B) --> Here our A = 7x and b = 6x. Just plug in and solve and then multiply whatever you get by 7/2 which we factored out earlier.

Answer 17

im sorry but how can you factor out a 7/2?