a little trig

by mercury
Tags: trig
Mar26-03, 04:13 AM
P: n/a
this is a question that was part of an mcq test.
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.
Phys.Org News Partner Science news on Phys.org
Going nuts? Turkey looks to pistachios to heat new eco-city
Space-tested fluid flow concept advances infectious disease diagnoses
SpaceX launches supplies to space station (Update)
Mulder is offline
Mar26-03, 05:02 AM
P: 115
Right, I'm assuming you know sin^2 +cos^2 = 1.

Well you can see this is nearly similar, and almost exactly the same if B = C. So there's two angles the same.

So now cos^2 + sinA sin^2 = 1

Which means sinA must be 1.

Therefore A can only take value of 90 degrees - right angle (450...etc useless here)

180 - 90..other two angles combine as total 90 degrees, so they must be 45 each since you've already found they're the same. Which leaves you a right angled isosceles.

Register to reply

Related Discussions
Trig Help Precalculus Mathematics Homework 7
trig help General Math 4
Trig Calculus & Beyond Homework 1
Trig help Precalculus Mathematics Homework 5
trig help Introductory Physics Homework 2