ITS A QUESTION OF TRIGNOMETRY U CAN DO IT BY USING IDENTITIES
2007-07-27 20:50:30 · 4 answers · asked by anshul j 1 in Science & Mathematics ➔ Mathematics
No you can't.
Take A=B =C= 0 since you put no restrictions on these
cos(0)=1 so -1 - 4cos(a)cos(b)cos(c) = -1 - 4 or -5
cos (2*0)=1 so cos(2a) + cos(2b) + cos(2c) = 3
And I don't think that 3 and -5 are the same
Did you possibly mean -1 + 4cos(a)cos(b)cos(c) ?????
Well if we take A=B=C=pi/2 so cos(A)=0 and cos(2A)=-1
Then we get -3 = -1. Again not good.
So just what do you mean?
Perhaps this is for a triangle so A + B + C add to 180 degrees?
2007-07-27 21:02:10 · answer #1 · answered by Captain Mephisto 7 · 1⤊ 1⤋
Gees and thought I had problems.
All I gotta do is work out the cost of bread and milk.
Good Luck !!!
2007-07-28 06:29:43 · answer #2 · answered by DaAussie@Australia 5 · 0⤊ 0⤋
I assume that A+B+C = 180
cos2A + cos2B + cos2C = 2cos(A+B).cos(A-B) + 2cos^2C -1
=2cos(180-C).cos(A-B) + 2cos^2C -1
= - 2cosC.cos(A-B) +2cos^2C -1
= -2cosC(cos(A-B) - cosC) -1
= -2cosC(cos(A-B) - cos(180-(A+B)) ) -1
= -2cosC(cos(A-B) + cos(A+B)) -1
= -2cosC( 2cosA.cosB) -1
= -4cosAcosBcosC -1
2007-07-30 11:24:45 · answer #3 · answered by Anubarak 3 · 1⤊ 0⤋
can you teach me how to do this?
2007-07-28 03:58:02 · answer #4 · answered by mammalia_monkey 4 · 0⤊ 2⤋