Question

if AB=6√3cm,AC=12cm and BC=6cm in ∆ABC What is the value of angle B ​

Answer 1

let AB=c=

$6 \sqrt{3} cm$

let BC=a=

$6cm$

let AC=b=

$12cm$

using cosine formula we get,

$\cos(b) = ( {a}^{2} + {c}^{2} - {b}^{2} ) \div 2ac \\ = ( ({6}^{2} ) + ({6 \sqrt{3} })^{2} - ( {12}^{2} )) \div (2 \times 6 \times 6 \sqrt{3} ) \\ = (36 + 108 - 144) \div (72 \sqrt{3)} \\ = 0 \\ cos(b) = 0 \\ b = 90degrees$