Asked by Jonathan
if cosA = 4/5; sin <0; cosB = 12/13; 0<B<90, determine sin(A-B)
thanks ... :)
thanks ... :)
Answers
Answered by
bobpursley
The first pairing says that sinA is -4/5
If cosB is 12/13, then sinB is 7/13
Sin(A-B)=CosASinB-SinACosB, right?
If cosB is 12/13, then sinB is 7/13
Sin(A-B)=CosASinB-SinACosB, right?
Answered by
Jonathan
yeah that's right, can u go on?
Answered by
bobpursley
I could, but I wont. However, I will be happy to critique your work or thinking
Answered by
bobpursley
Error: sinA=-3/5
in all cases, sin^2 Theta + cos^2 Theta=1
Answered by
Jonathan
well, i got:
(-4/5)(12/13) - (4/5)(7/13)
therefore
(-48/65) - (28/65)
therefore:
answer = (-76/65)
(-4/5)(12/13) - (4/5)(7/13)
therefore
(-48/65) - (28/65)
therefore:
answer = (-76/65)
Answered by
Reiny
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)
= -56/65
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)
= -56/65
Answered by
bobpursley
change the Sin A in the first term, and it works.
Answered by
Jonathan
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
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
Answered by
bobpursley
In any angle, the sum of the squares of the cosines and sines is equal to one. Use that to solve.
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