Find the Exact Value of the Expression Using the Provided $\cos ( \mathrm { s } + \mathrm { t } )$

question 25

Multiple Choice

Find the exact value of the expression using the provided information.
-Find $\cos ( \mathrm { s } + \mathrm { t } )$ given that $\cos \mathrm { s } = - \frac { 1 } { 2 }$ , with s in quadrant III, and $\cos t = - \frac { 3 } { 5 }$ , with $\mathrm { t }$ in quadrant III.

• A) \(\frac { - 3 - 4 \sqrt { 3 } } { 10 }\)
• B) \(\frac { 3 - 4 \sqrt { 3 } } { 10 }\)
• C) \(\frac { 3 + 4 \sqrt { 3 } } { 10 }\)
• D) \(\frac { 3 - 4 \sqrt { } } { 10 }\)

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