#### mercury

and i did'nt have any clue as to how to begin!

finally i just tried plugging in values for A,B,C to see if they worked.

for ex. i put A=B=C=60 (degrees)- equilateral and so on..but i'd like to know the logical way to do it...

if A,B,C are the vertices of a triangle,

and if cosBcosC + sinAsinBsinC = 1

is the triangle

a) equilateral

b) isosceles

c) right angled isosceles

d) right angled but not isosceles

e) none of the above.