Trig Help !

[bipster10]

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Hey guys...
I am just looking over some QR problems and I need help with a trig type of problem that I know the DAT just lovees to ask. This example I got from Destroyer...

cos(116 ) =

a cos(64)
b tan(64)
c sin (64)
d sec (64)
e -cos(64)

All of the numbers are in degrees btw. Also, I somewhat understand his explanation ( I think ) but I just need to know alternate explanations or someone to just explain it a little better. Thanks guys!

 

[slm266]

E. -cos 64

for trig, I always use the unit circle divided in quadrants (see attachment).

The cosine of an angle in quadrant II will be equal to the - cosine of the complimentary angle (116-90=64) in quad I.

Other correct answers could have been cos 244 or - cos 296.

 

[nainaaz]

Hey guys...
I am just looking over some QR problems and I need help with a trig type of problem that I know the DAT just lovees to ask. This example I got from Destroyer...

cos(116 ) =

a cos(64)
b tan(64)
c sin (64)
d sec (64)
e -cos(64)

All of the numbers are in degrees btw. Also, I somewhat understand his explanation ( I think ) but I just need to know alternate explanations or someone to just explain it a little better. Thanks guys!

quick answer to choose will be choice E
116 degrees is in II quadrant and only SINE function is positive. all other functions will be negative.

Question.... cos (116)= negative value (180-116=64) for cosine in QII

A) cos(64) positive value (should have been negative)
B) tan (64) positive value (should have been negative)
C) sin (64) positive value but..(it would have been right when sin=(90-cos) which is 90-64= 26)
D) sec (64) no func
E) -cos (64) negative value

Hope it helps 🙂

 

[wanttobedmd]

CAST

The post above is such a valid explanation 🙂

 

[bipster10]

Well thanks I think i understand the CAST thing for the most part...but if the angle would end up in the third quadrant (tan) which trig functions would be negative in that case?...I hope that made sense hahah

 

[Ibracadabra]

Well thanks I think i understand the CAST thing for the most part...but if the angle would end up in the third quadrant (tan) which trig functions would be negative in that case?...I hope that made sense hahah

both sin and cos will be negative in the third quadrant 🙂

 

[slm266]

It's exactly like an XY coordinate system. Think of your x movement as cosine, and y movement as sine.
Quad I: +c, +s (1-89 degrees)
Quad II: -c, +s (91-179)
Quad III: -c, -s (181-269)
Quad IV: +c, -s (271-359)

if that didn't make sense, study my diagram in my first post.

if you can understand that conceptually, and memorize the few values, you should be able to do trig problems very quickly.

 

[bipster10]

Thanks a lot guys...this will help out a lot!!!