AonZ
  • AonZ
HELP PLEASE!!! ABCD is a cyclic quadrilateral in which AB=5. BC=6. CD=7. AD=8. show that cos ADC = 13/43
Mathematics
  • Stacey Warren - Expert brainly.com
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SOLVED
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katieb
  • katieb
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AonZ
  • AonZ
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AonZ
  • AonZ
@kropot72 @terenzreignz @Mertsj Help pls Btw i know angles D+B = 180
AonZ
  • AonZ
@hartnn help please!!!

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Mertsj
  • Mertsj
There is a formula for this. First let me relabel your picture so you will understand the formula better.
AonZ
  • AonZ
ok... only formula i know is angle B + D=180 and angle A+C = 180
Mertsj
  • Mertsj
|dw:1367022862806:dw|
Mertsj
  • Mertsj
\[\cos A=\frac{a^2+d^2-b^2-c^2}{2(ad+bc)}\]
Mertsj
  • Mertsj
Just plug into the formula.
AonZ
  • AonZ
yes!!! that actually worked!! Thank you so much
Mertsj
  • Mertsj
yw
hartnn
  • hartnn
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
AonZ
  • AonZ
ohhhh i see

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