AP EAMCET · Maths · Properties of Triangles
In a \(\triangle A B C, a=6, b=5\) and \(c=4\), then \(\cos 2 A=\)
- A \(-\frac{31}{32}\)
- B \(-\frac{15}{16}\)
- C \(\frac{31}{32}\)
- D \(\frac{15}{16}\)
Answer & Solution
Correct Answer
(A) \(-\frac{31}{32}\)
Step-by-step Solution
Detailed explanation
In a \(\triangle A B C, a=6\) units, \(b=5\) units and \(c=4\) units As we know that, \(\cos A=\frac{b^2+c^2-a^2}{2 b c}\) \(\Rightarrow \cos A=\frac{b^2+c^2-a^2}{2 b c}=\frac{5^2+4^2-6^2}{2 \times 5 \times 4}=\frac{1}{8}\) As we know that, \(\cos 2 A=\cos ^2 A-\sin ^2 A\)…
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