Question

Plz help me solving this ​

Answer 1

Answer: (-16/65)  

Step-by-step explanation:

sin A = 12/13

cos A = √1-(12/13)²

          = √1 - 144/169

          = √25/169

          = 5/13

∵the angle are obtuse so, cos A = -5/13

Answer 2

Now, cos(A+B) = cosAcosB - sin A sin B = (5/13)(-4/5) - (12/13)(3/5) = -56/65 [Ans.]

I hope my answer will come to use assuming my answer is correct. Feel free to give your remark response to me.