Question

In ΔABC, if a = 18, b = 24, c = 30 then find the values of cos `A/2`

Answer 1

Given: a = 18, b = 24 and c = 30
∴ 2s = a + b + c
= 18 + 24 + 30
= 72
∴ s = 36
`cos  "A"/(2) = sqrt((s(s - a))/(bc)`

= `sqrt((36(36 - 18))/((24)(30)`

= `sqrt((36 xx 18)/(24 xx 30)`

= `sqrt(9/10)`

= `(3)/sqrt(10)`.