Find cos B exactly if a = 15, b = 11, and angle C is a right triangle choices; a) 15/11 b) 11/15 c) sqrt346/15 d) 15/sqrt346

The major trigonometric ratios at this level include sine, cosine and tangent.
sine is the ratio of opposite to hypotenuse, cosine is the ratio of adjacent to hypotenuse while tan is the ratio of opposite to adjacent. Therefore, in this case our adjacent is 15, To get the hypotenuse we use the pythagoras theorem 
15² + 9² = 346, thus the hypotenuse will be √346.
Hence, cos B will be 15/√346