Given sina=6/7 and cosb=-1/6, where a is in quadrant ii and b is in quadrant iii , find sin(a+b) , cos(a-b) and tan(a+b)

now, keep in mind that, the hypotenuse is just a radius unit, and thus is never negative, so if a fraction with it is negative, is the other unit.  A good example of that is the second fraction here, -1/6, where the hypotenuse is 6, therefore the adjacent side is -1.  Anyhow, let's find the opposite side to get the sin(b).



now











and now, let's rationalize the denominator of that one, hmmm let's see

P(chicago, illinois)