In triangle ABC, AB = AC and D is a point on BC. If BD = 5 cm, AB = 12 cm and AD = 8 cm, then the length of CD is:
Show answer & explanation
Correct answer: C
Explanation
The correct answer is option 3 i.e. 16.
Applying cosine rule:
cos θ = 
⇒ 21x = 80 + x2
⇒ x2 - 21x + 80 = 0
⇒ (x - 16) (x - 5) = 0
⇒ x = 16 as x ≠ 5
Hence,
CD = 16 cm