Answers

2015-07-29T19:35:21+05:30
Let ab side be denoted by c, bc by a and ca by b.
angle a be denoted as A.
now, the formula,
cosA=b^2+c^2-a^2/2bc
cosA is cos60=1/2
put it in the equation.
you will get a^2=c^2+b^2-bc.
hence proved.
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