# Thread: I need help with trig!

1. ## I need help with trig!

Hi i really really need to answer these last two questions by the next 30minutes!! (i have online math) can anyone help me?

Use the formulas for functions of the difference and sum of two angles to find, without tables or calculator, the cosine, sine, and tangent of 15degrees(using 45degrees and 30degrees) tan 15degrees=?

Using the given data, find the values of the sine, cosine, and tangent of ( AB) and of (A - B). Give the quadrant in which each of the angles (A + B) and (A - B) terminates:
angle A in Quadrant II, tan A=-12/5

+ angle B in Quadrant III, sin b=-3/5
sin a-b=?

2. Originally Posted by moneyca
Hi i really really need to answer these last two questions by the next 30minutes!! (i have online math) can anyone help me?

Use the formulas for functions of the difference and sum of two angles to find, without tables or calculator, the cosine, sine, and tangent of 15degrees(using 45degrees and 30degrees) tan 15degrees=?

Using the given data, find the values of the sine, cosine, and tangent of ( AB) and of (A - B). Give the quadrant in which each of the angles (A + B) and (A - B) terminates:
angle A in Quadrant II, tan A=-12/5

+ angle B in Quadrant III, sin b=-3/5
sin a-b=?
I'm not the trig guru on this forum, but this is what you need: $45\deg-30\deg=15\deg$

$\sin(s-t)=\sin s \cos t- \cos s \sin t$

$\cos(s-t)=\cos s cos t+\sin s sin t$

$\tan(s-t)=\frac{\tan s-\tan t}{1+\tan s \tan t}$