Question

In ΔABC if a = 13, b = 14, c = 15, then find the value of sec A.

Answer 1

Using the cosine rule:

cos A = `(b^2 + c^2 - a^2)/(2bc)`

= `(14^2 + 15^2 - 13^2)/(2(14)(15))`

= `(196 + 225 - 169)/420`

= `252/420`

= `3/5`

sec A = `1/cos A`

= `1/(3/5)`

= `5/3`

= 1.67