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

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AonZBest ResponseYou've already chosen the best response.0
@kropot72 @terenzreignz @Mertsj Help pls Btw i know angles D+B = 180
 11 months ago

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

AonZBest ResponseYou've already chosen the best response.0
ok... only formula i know is angle B + D=180 and angle A+C = 180
 11 months ago

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

MertsjBest ResponseYou've already chosen the best response.2
Just plug into the formula.
 11 months ago

AonZBest ResponseYou've already chosen the best response.0
yes!!! that actually worked!! Thank you so much
 11 months ago

hartnnBest ResponseYou've already chosen the best response.1
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
 11 months ago
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