Question

In triangle ABC AB =AC= 15cm and BC =18cm find cos ABC

Answer 1

Hi!

Here is the answer to your question.

 

The sides of ΔABC are AB = AC = 15 cm and BC = 18 cm.

AB2 + AC2 = (15 cm)2 + (15 cm)2 = 225 cm2 + 225 cm2 = 450 cm2

BC2 = (18 cm)2 = 324 cm2

∴ AB2 + AC2 ¹ BC2

⇒ ΔABC is not a right triangle.

∴We cannot find the values of cos ∠ABC and sin ∠ACB by directly using trigonometric ratio.

For this you need to know cosine law

Answer 2

The sides of ΔABC are AB = AC = 15 cm and BC = 18 cm.
AB2 + AC2 = (15 cm)2 + (15 cm)2 = 225 cm2 + 225 cm2 = 450 cm2
BC2 = (18 cm)2 = 324 cm2
∴ AB2 + AC2 ¹ BC2
⇒ ΔABC is not a right triangle.
∴We cannot find the values of cos ∠ABC and sin ∠ACB by directly using trigonometric ratio.