Question

if 
(x - \frac{1}{2x} = 3)(x−2x1​=3) 
find the value of

{x}^{2} + \frac{1}{4 {x}^{2} }x2+4x21​ 
i have solution in the picture but i have a doubt that why have we used the formula

( {a}^{2} + {b}^{2} - 2ab) = (a - b)^{2}(a2+b2−2ab)=(a−b)2 
instead of

(a - \frac{1}{a} )^{2} = {a}^{2} + \frac{1}{a}^{2} - 2(a−a1​)2=a2+a1​2−2 
give the reason and in case if we can use both then give the solution with other one
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Answer 1

ek the first place and it will take you off of a good weekend so that the other one or both in this message was automatically generated by the way I can get a 22211