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).

Answer 1

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

Answer 2

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

Answer 3

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

Answer 4

Oh, okay. Thank you! :)

Answer 5

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

Answer 6

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

Answer 7

Thanks!!!! :D

Answer 8

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

Answer 9

no probs dear