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A square of a binomial is shown as:
(a+b)² = a²+2ab+b²
(a-b)² = a²-2ab+b²
1. x²+36 = x²+0+6² ≠ (x+6)² 
is not a square since we do not have a middle term which is supposed to be 12x.

2. 4x²-10x+9 = (2x)²-2(5x)+3² ≠ (2x-3)² since the middle term must be -12x.