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HELP PLEASE!!! ABCD is a cyclic quadrilateral in which AB=5. BC=6. CD=7. AD=8. show that cos ADC = 13/43

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@kropot72 @terenzreignz @Mertsj Help pls Btw i know angles D+B = 180
@hartnn help please!!!

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Other answers:

There is a formula for this. First let me relabel your picture so you will understand the formula better.
ok... only formula i know is angle B + D=180 and angle A+C = 180
\[\cos A=\frac{a^2+d^2-b^2-c^2}{2(ad+bc)}\]
Just plug into the formula.
yes!!! that actually worked!! Thank you so much
did you get how how found cos A ? he just applied cosine rule, twice. once in triangle ABD and then in triangle BCD, also knowing A+C = 180, so cos C = -cos A
ohhhh i see

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