1.

cos ^(2) ((A)/(2))+ cos ^(2) ((B)/(2))+cos ^(2)(( C )/(2))=

Answer»

` 1- ( r )/( R ) `
` 1- ( R )/( r ) `
` 2+ (r ) /( 2 R) `
` 1 - ( r ) /(2R ) `

ANSWER :C


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