Diketahui segitiga ABC dengan panjang AB=6√3cm BC=6cm AC=6cmTentukan:besar sudut A​

AB = c = 6√3 cm

BC = a = 6 cm

AC = b = 6 cm

<A =?

a² = b² + c² – 2bc.cos A

6² = 6² + (6√3)² – 2.6.6√3.cos A

36 = 36 + 108 – 72√3.cos A

36 = 144 – 72√3.cos A

36-144 = -72√3.cos A

-108 = -72√3.cos A

-108/-72√3 = cos A

3/2√3 = cos A

rasionalkan nilai dari 3/2√3:

3/2√3 x 2√3/2√3

= 6√3 / 12

= √3/2

√3/2 = cos A

A = arccos (√3/2)

A = 30°