Answer
$8^{2}$ = $(6)^{2}$ + $(9)^{2}$ - 2*6*9*cos β
Work Step by Step
Given data
a=6,b =8, c=9
Using theorem 11.4.3
In triangle ABC
$b^{2}$ = $a^{2}$ + $c^{2}$ - 2ac cos β
$8^{2}$ = $(6)^{2}$ + $(9)^{2}$ - 2*6*9*cos β
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