Q.compound angles trig. (1 Viewer)

[freaking_out]

i think this has a very easy answer to to but i just seem to have a mindblock with this one:

if sinA=2/3 and cosB=1/4, where A and B are acute angles, find cos(A-B)...


thnx in advance

 

[kini mini]

Originally posted by freaking_out
i think this has a very easy answer to to but i just seem to have a mindblock with this one:

if sinA=2/3 and cosB=1/4, where A and B are acute angles, find cos(A-B)...

IIRC....

cos(A-B) = cosA.cosB + sinA.sinB

and where A and B are acute, you can use Pythagoras to find the complementary trig ratios of A and B

 

[freaking_out]

use Pythagoras to find the complementary trig ratios

oh crap, now i remember!!! i was trying to expand cos(90-A) and i kept on getting sin A. :mad1:

 

[kini mini]

Originally posted by freaking_out


i was trying to expand cos(90-A) and i kept on getting sin A. :mad1:

That's alright - I'd be worried if you got anything else