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Find the measure of angle A in degrees.Option 1: 135°Option 2: 140°Option 3: 120°Option 4: 60°

Find the measure of angle A in degrees.Option 1: 135°Option 2: 140°Option 3: 120°Option-example-1
User Hugo Reyes
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1 Answer

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To solve this problem, we use the Law of Cosines.

Using the Law of Cosines, we get that:


2√(13)=√(2^2+6^2-2(2)(6)cosA).

Solving the above equation for cosA, we get:


\begin{gathered} 4(13)=4+36-24cosA, \\ 52=40-24cosA, \\ 24cosA=-12, \\ cosA=(-12)/(24)=-(1)/(2). \end{gathered}

Therefore:


A=120^(\circ).

Answer:


\begin{equation*} 120^(\circ). \end{equation*}

User Julius
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