1.

A : sum_(r=1)^(n-1) cos^(2) (rpi)/(n)=(n)/(2)-1 R :cos alpha + cos ( alpha + beta ) + cos (alpha + 2 beta ) + ......... + cos ( alpha + (n-1)beta ) = (sin(nbeta //2))/(sin ( beta//2)) cos""((2alpha + (n-1) beta )/(2))

Answer»

A is TRUE , R is true and R is correct EXPLANATION of A
A is true , R is trueand R is not correct explanation of A
A is true , R is FALSE
A is false , R is true

ANSWER :A


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