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Question
If a = 13, b = 14, c = 15, then `cos("A"/2)` = ______.
Options
`1/sqrt(5)`
`2/sqrt(5)`
`1/2`
`1/5`
MCQ
Fill in the Blanks
Solution
If a = 13, b = 14, c = 15, then `cos("A"/2)` = `2/sqrt(5)`.
Explanation:
s = `("a" + "b" + "c")/2 = (13 + 14 + 15)/2` = 21
`cos ("A"/2) = sqrt(("s"("s" - "a"))/"bc"`
= `sqrt((21(21 - 13))/(14 xx 15)`
= `sqrt(4/5)`
= `2/sqrt(5)`
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