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AonZ
 one year ago
HELP PLEASE!!!
ABCD is a cyclic quadrilateral in which AB=5. BC=6. CD=7. AD=8. show that cos ADC = 13/43
AonZ
 one year ago
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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AonZ
 one year ago
Best ResponseYou've already chosen the best response.0@kropot72 @terenzreignz @Mertsj Help pls Btw i know angles D+B = 180

Mertsj
 one year ago
Best ResponseYou've already chosen the best response.2There is a formula for this. First let me relabel your picture so you will understand the formula better.

AonZ
 one year ago
Best ResponseYou've already chosen the best response.0ok... only formula i know is angle B + D=180 and angle A+C = 180

Mertsj
 one year ago
Best ResponseYou've already chosen the best response.2\[\cos A=\frac{a^2+d^2b^2c^2}{2(ad+bc)}\]

Mertsj
 one year ago
Best ResponseYou've already chosen the best response.2Just plug into the formula.

AonZ
 one year ago
Best ResponseYou've already chosen the best response.0yes!!! that actually worked!! Thank you so much

hartnn
 one year ago
Best ResponseYou've already chosen the best response.1did 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
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