posted by Jonathan on .
if cosA = 4/5; sin <0; cosB = 12/13; 0<B<90, determine sin(A-B)
thanks ... :)
The first pairing says that sinA is -4/5
If cosB is 12/13, then sinB is 7/13
yeah that's right, can u go on?
I could, but I wont. However, I will be happy to critique your work or thinking
in all cases, sin^2 Theta + cos^2 Theta=1
well, i got:
(-4/5)(12/13) - (4/5)(7/13)
(-48/65) - (28/65)
answer = (-76/65)
from if cosA = 4/5; sin <0 we know that A is in the fourth quadrant and sinA = -3/5
from cosB = 12/13; 0<B<90 we know sinB = 5/13
sin(A-B) = sinAcosB - cosAsinB
= (-3/5)(12/13) - (4/5)(5/13)
change the Sin A in the first term, and it works.
i knew that was wrong, coz my answer should be in the 50's haha..thanks though, great help
can i ask how you got sinA and sinB with that information :)
no point in me just copying it i would like to know how you got it
In any angle, the sum of the squares of the cosines and sines is equal to one. Use that to solve.