If $sin α = \frac{4}{5}$ $sinalpha=4/5$ and $α$ $alpha$ is obtuse angle, what is $cos α$ $cosalpha$ ?

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If $sin α = \frac{4}{5}$ $sinalpha=4/5$ and $α$ $alpha$ is obtuse angle, what is $cos α$ $cosalpha$ ?

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Answer 1 · 2017-03-02T16:30:53

$cos α = - \frac{3}{5}$ $cosalpha=-3/5$

Explanation:

As $α$ $alpha$ is obtuse, it lies in second quadrant and $cos α$ $cosalpha$ will be negative.

Now $sin α = \frac{4}{5}$ $sinalpha=4/5$ and therefore

$cos α = - \sqrt{1 - {(\frac{4}{5})}^{2}} = - \sqrt{1 - \frac{16}{25}} = - \sqrt{\frac{9}{25}} = - \frac{3}{5}$ $cosalpha=-sqrt(1-(4/5)^2)=-sqrt(1-16/25)=-sqrt(9/25)=-3/5$

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If $sin α = \frac{4}{5}$ $sinalpha=4/5$ and $α$ $alpha$ is obtuse angle, what is $cos α$ $cosalpha$ ?

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