Find the Exact Values of the Indicated Trigonometric Functions $\cos B$

Multiple Choice

Find the exact values of the indicated trigonometric functions. Write fractions in lowest terms.
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Find $\cos B$ and $\cot B$ .

A) $\cos B = \frac { a } { c } ; \cot B = \frac { a } { b }$
B) $\cos B = \frac { c } { a } ; \cot B = \frac { b } { a }$
C) $\cos \mathrm { B } = \frac { \mathrm { c } } { \mathrm { b } } ; \cot \mathrm { B } = \frac { \mathrm { a } } { \mathrm { b } }$
D) $\cos B = \frac { b } { c } ; \cot B = \frac { b } { a }$