if in a triangle ABC, cosA.cosB+sinAsinBsinC=1, then the triangle is
a) right angled
b) equilateral
c)isosceles
d)none

Question

anonymous · Answer

a)
use A=B and C=90
u get (sinA)^2+(cosA)^2=1 which is an identity!

anonymous · Answer

its not necessary that A should be equal to B right?

anonymous · Answer

the answer is d

anonymous · Answer

that gives a 45-90-45 triangle.
i JUst tested a PARTICULAR case
the answer should hold for all cases!!

anonymous · Answer

k. then guessing wont work..

anonymous · Answer

you want to see the solution?

anonymous · Answer

yups...

anonymous · Answer

why ask if u know the solution?

anonymous · Answer

because i dont understand them.

anonymous · Answer

why dont u use transformation formulae with the result A+B+C=180
that will give you the answer.

anonymous · Answer

okay i got that one cleared up...thanx

anonymous · Answer

how?

anonymous · Answer

jus took out sinC from the relation.. that led to to the conclusion that A=B
and finally C=90
the answer should be a
its misprinted here i guess

anonymous · Answer

well guess was right. It had to be right you know!!