Question

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

Answer 1

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

Answer 2

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

Answer 3

the answer is d

Answer 4

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

Answer 5

k. then guessing wont work..

Answer 6

you want to see the solution?

Answer 7

yups...

Answer 8

why ask if u know the solution?

Answer 9

because i dont understand them.

Answer 10

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

Answer 11

okay i got that one cleared up...thanx

Answer 12

how?

Answer 13

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

Answer 14

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