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Question : 117 of 160
Marks:
+1,
-0
Solution:
Let
=2−+,‌‌=−3−5 and
=3−4−4 ∴‌‌a=||=√6,b=||=√35 and
‌‌c=||=√41∴‌‌cos‌A‌=‌‌=‌| (√35)2+(√41)2−(√6)2 |
| 2√35√41 |
⇒‌‌cos‌A‌=‌=√‌⇒cos2A‌=‌
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