In `A B C` , prove that `cosA+cosB+cosClt=3/2dot`

Prove tha acosA+bcosB+c cosClt=sdot

Prove that cosA+cosB+cosC=1+r/R

Prove that cos3A=4cos^3 A-3cosA

Prove that (b+c)cosA+(c+a)cosB+(a+b)cosC=2sdot

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

In triangle A B C , prove that sin(A/2)+sin(B/2)+sin(C/2)lt=3/2dot Hence, deduce that cos((pi+A)/4)cos((pi+B)/4)cos((pi+C)/4)lt=1/8

In a /_\A B C , if tanA/2,tanB/2,tanC/2"are in"AdotPdot, then show that cosA ,cosB ,cosC are in AdotPdot

In A B C , prove that (a-b^2cos^2C/2+(a+b)^2sin^2C/2=c^2dot

Prove that ("a c o s"A+b cosB+ccosC)/(a+b+c)=r/Rdot