Question

If a = 13, b = 14, c = 15, then `cos("A"/2)` = ______.

विकल्प

• `1/sqrt(5)`

• `2/sqrt(5)`

• `1/2`

• `1/5`

Answer 1

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)`