Question

2 cos a cos B

is equal to what identity?

Answer 1

\[\cos(a+b) + \cos(a-b)\]

Answer 2

I mean like this, 2 cos α cos β = 2 (_________)

Answer 3

yea.. thats what i meant..
\[2cosAcosB= \cos(A+B) +\cos(A-B)\]

Answer 4

what would i put on my blank?

Answer 5

you think and tell

for eg..
\[3 = \frac{1}{2}( ....)\]
what will be in the blank!?

Answer 6

in the blank cos(a+b)+cos(a-b)

Answer 7

have no idea. the equsation on my book is indded what you have said, but my online assignment is asking for thw blank

Answer 8

yea i know.. can you think? :)

first answer my example question

Answer 9

2 cos a cos b = cos(a+b)+cos(a-b)

2 cos a cos b = 2 (____________ )
= cos(a+b)+cos(a-b)

Answer 10

yea.. you are so close.. :P.. if u answer my question.. u will be able to answer ur question too!

Answer 11

is it 2 ?

Answer 12

If \(2X=Y\) then \(2X=2\left(\dfrac{Y}{???}\right)\)

Answer 13

x ?

Answer 14

\[5\ apples = \frac{10\ apples}{???}\]

Answer 15

2

Answer 16

so similarly

if i said

\[3\ apples = \frac{(???)\ apples}{3}\]

Answer 17

9 apples?

Answer 18

put nine.. there.. and tell me is that right answer? :P

Answer 19

9/3 = 3

Answer 20

so it is..correct :)

now similarly

i can say

\[3X = \frac{?X}{2}\]

Answer 21

6 :)

Answer 22

and finally think in similar manner and tell me

\[\cos(a+b)+\cos(a-b) = 2[(??) \cos(a+b) + \cos(a-b)]\]

Answer 23

1/ 2 !

Answer 24

Bingo!..

Answer 25

thank you!

Answer 26

your welcome :)!

Answer 27

for the patience :) :D

Answer 28

no problem.. i am a teacher.. i have tons of patience :D :D

Answer 29

:)))

Answer 30

Amen to that, @mashy! :)

Just make sure you have one more set of parens in that expression:

\(\Large \cos(a+b)+\cos(a-b) = 2[(??) \color{red}(\cos(a+b) + \cos(a-b)\color{red})]\)

:)

Answer 31

Yup I made sure, thanks debbieG :)