In a `/_\ABC , cosec A[sinB.cosC+cosB.sinC]=`
(A) `c/a`
(B) `a/c`
(C) 1
(D) none of these

If in a /_\ ABC, cosA.cosB+sinA.sinB.sinC =1,then (A) A=B (B) C=pi/2 (C) AC=BC (D) AB=sqrt(2) AC

cosA+cosB+cosC is equal to (A) r/R (B) R/r (C) 1 (D) 1+r/R

In any A B C ,2(bc cosA+ ca cosB+ab cosC) =

In triangle ABC, if cosA+2cosB+cosC=2,t h e na ,b ,c are in (A) A.P. (B) G.P. (C) H.P. (D) none of these

If A+B+C=0 , then the value of sin^2A+cosC(cosAcosB-cosC)+cosB(cosAcosC-cosB) is equal to: -1 (b) 0 (c) 1 (d) none of these

If angle C of a triangle ABC be obtuse, then (A) 0 1 (C) tan A tan B=1 (D) none of these

If A+B+C=pi , prove that : cosA + cosB-cosC=4cos(A/2) cos(B/2) sin(C/2) -1

If A,B,C, are the angles of a triangle such that cot(A/2)=3tan(C/2), then sinA ,sinB ,sinC are in (a) AdotPdot (b) GdotPdot (c) HdotPdot (d) none of these

If A+C=2B, then (cosC-cosA)/(sinA-sinC)=

a(cosC-cosB)=2(b-c)cos^2A/2