in the diagram (attached), ABCD is a quadrilateral where AD parallel to BC. it is given that AB=9, BC=6, CA=5 and CD=15.(adsbygoogle = window.adsbygoogle || []).push({});

show that cos BCA=-1/3 and hence find the value of sin BCA

i can do the 'show that' bit but i don't know how to find sinBCA. any help??

also when evaluating log15 + log20 - log12 (all to the base 5) do you do the addition to multiplication conversion first or the subtraction to division first?

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# Dodgy trig question

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