If x&y be real, show that the equation sin2θ=(x2+y2)/2xy is possible only when x=y is not equal to zero.
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Solution
sin2θ=(x2+y2)2xy We know, (x−y)2=x2+y2−2xy If (x−y)2=0⇒x=y ⇒x2+y2=2xy ⇒x2+y22xy=1 Also, x&y should not be equal to 0, otherwise it will be of the form 10 which is not defined.