# From (1),Example 9. If ABCD is a cyclic quadrilateral, prove thatcos A + cos B + cos C + cos D = 0.Solution. Since ABCD is a cyclic quadrilateralA+ C = 180Â° and B + D = 180Â°L.H.S. = cos A + cos B + cos C + cos D= cos A + cos B + cos (180Â° - A) + cos (180Â°-B)= cos A + cos B - cos A - cos B = 0 = R.H.S.Example 10. In any quadrilateral ABCD, prove thatsin (A+B) + sin (C+D) = 0cos (A + B) = cos (C+D)Solution. Since ABCD is a quadrilateralA + B + C + D = 2 = A + B = 27 - (C+D)?

## Most Viewed Questions

### Preparation Products

##### Knockout NEET May 2023 (Easy Installments)

Personalized AI Tutor and Adaptive Time Table, Self Study Material, Weekend Live Classes, Mentorship from our Experts, Unlimited Mock Tests and Personalized Analysis Reports, 24x7 Doubt Chat Support,.

₹ 5499/-
##### Knockout JEE Main April 2021 (One Month)

Personalized AI Tutor and Adaptive Time Table, Self Study Material, Weekend Live Classes, Mentorship from our Experts, Unlimited Mock Tests and Personalized Analysis Reports, 24x7 Doubt Chat Support,.

₹ 14000/- ₹ 4999/-
##### Knockout NEET Aug 2021 (One Month)

Personalized AI Tutor and Adaptive Time Table, Self Study Material, Weekend Live Classes, Mentorship from our Experts, Unlimited Mock Tests and Personalized Analysis Reports, 24x7 Doubt Chat Support,.

₹ 14000/- ₹ 4999/-
##### Knockout JEE Main May 2021

Personalized AI Tutor and Adaptive Time Table, Self Study Material, Weekend Live Classes, Mentorship from our Experts, Unlimited Mock Tests and Personalized Analysis Reports, 24x7 Doubt Chat Support,.

₹ 22999/- ₹ 9999/-