Prove

Asked by  | 4th Jul, 2008, 09:30: PM

Expert Answer:

the quadrilateral is cyclic.

thus, sum of opposite angles of the quadrilateral is 180o.

that is, A+C = 180 and B+D = 180

consider L.H.S.,

cos(180-A) + cos(180+B) + cos(180+C) - sin(90+D)

= -cosA-cosB-cosC-cosD

= - [cosA+cosC] - [CosB+cosD]

Answered by  | 15th Jul, 2008, 09:48: AM

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