Two Sides of a Right Triangle ABC (C Is the Right

Multiple Choice

Two sides of a right triangle ABC (C is the right angle) are given. Find the indicated trigonometric function of the given
angle. Give exact answers with rational denominators.
-Find $\cos \mathrm { A }$ when $\mathrm { a } = \sqrt { 13 }$ and $\mathrm { c } = 10$ .

A) $\frac { 13 } { 10 }$
B) $\frac { \sqrt { 87 } } { 10 }$
C) $\frac { 87 } { 13 }$
D) $\frac { \sqrt { 13 } } { 10 }$