Hi everyone.....

I have a problem that say:

if ( 1-8*cos(a)*cos(b)*cos(c)=0) then (a=b=c=60 degree)

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I solved it

1-8*cos(a)*cos(b)*cos(c)=

1 - 8*cos A cos B cos C =1 - 4*cos A * [cos (B-C) + cos (B+C)]=[sin (B-C)]^2 + [cos (B-C)]^2 - 4*cos (A) cos (B - C) + 4*[cos A]^2 =[sin (B-C)]^2 +[cos (B-C) - 2*cos A]^2 >=0********************************

but they said that when 1-8*cos A * cos B * cos C=0

that mean a=b=c=60 deg

?????

how can i handle this problem.?