Question #fca5d

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Answer 1 · 2017-04-17T08:37:01

$θ = \frac{π}{2}$ $"theta=pi/2$

$you can use the cosine law.$ $"you can use the cosine law."$
$r^{2} = a^{2} + b^{2} + 2 a b \cdot cos θ$ $r^2=a^2+b^2+2ab*cos theta$

$15^{2} = 9^{2} + 12^{2} + 2 \cdot 15 \cdot 9 \cdot cos θ$ $15^2=9^2+12^2+2*15*9*cos theta$

$225 = 81 + 144 + 270 \cdot cos θ$ $225=81+144+270*cos theta$

$225 = 225 + 270 \cdot cos θ$ $225=225+270*cos theta$

$225 - 225 = 270 \cdot cos θ$ $225-225=270*cos theta$

$0 = 270 \cdot cos θ$ $0=270*cos theta$

$cos θ = 0$ $cos theta =0$

$a r c cos (0) = \frac{π}{2}$ $arc cos( 0)=pi/2$

$θ = \frac{π}{2}$ $theta=pi/2$