Question

Find all values of theta between 0 and 360 that satisfy cos(theta)=-.73

Answer 1

$cos\theta=-0.73\\\\-cos\theta=0.73\\\\cos(180^o-\theta)=0.73\ or\ cos(180^o+\theta)=0.73\\\\180^o-\theta=43^o\ or\ 180^o+\theta=43^o\\\\\theta=137^o\ or\ \theta=-137^o\to\theta=-137^o+360^o=223^o\\\\Answer:\theta=137^o\ or\ \theta=223^o$