Page 121 - Math SL HB Sem 1

CIRCULAR FUNCTIONS AND TI{IGONONIE'IRY

The cosine rule

For any triangle ABC,

a2 = b2 +c2 - 2bc cosA
b' :a2 +c2 - 2accosB

c' =a' + b2 - 2abcosC

The cosine rule is used to solve a (non-right-angled) triangle if we are given
. the lengths ofits three sides
" the lengths oftwo sides and the measure ofthe included angle

Example l: In triangle ABC if a - 12 cm, b: 20 cm and c - 14 cm, lind
A,BandC

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