Write the product (5 sin 3pi/4)(cos 7pi/4) as a sum or difference.
How would I do this problem?
I know the answer, but I don't know how to do it.
The answer is: 5/2 (sin 5pi/2 - sin pi).

Question

Write the product (5 sin 3pi/4)(cos 7pi/4) as a sum or difference.
How would I do this problem? 
I know the answer, but I don't know how to do it.
The answer is: 5/2 (sin 5pi/2 - sin pi).

anonymous · Answer

use
 2sinacosb =sin (a+b) - sin(a-b)

anonymous · Answer

5/2 *2 sin 3pi/4)(cos 7pi/4

anonymous · Answer

here a= 7pi/4 and b = 3pi/4
thus a+b=5pi/2 and a-b = 4pi/4=pi

anonymous · Answer

Oh, okay. Thank you! :)

raden · Answer

it should  2sinacosb =sin (a+b) + sin(a-b)
@matricked

anonymous · Answer

@RadEn
yup u r correct dear but the above also works as b>a

anonymous · Answer

Thanks!!!! :D

raden · Answer

sorry, @matricked
i didny see, ur coment that a= 7pi/4 and b = 3pi/4 :)

anonymous · Answer

no probs dear