Question

$(2q - 3z) { }^{2} - 2(2q - 3z)(q - 3z) + (q - 3z) {}^{2}$
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Answer 1

Answer:

$(x - y) {}^{2} = {x}^{2} - 2xy + {y}^{2} \\ \\ here \: x = 2q - 3z \\ y = q - 3z$

so your answer is

$(2q - 3z) { }^{2} - 2(2q - 3z)(q - 3z) + (q - 3z) {}^{2}$

$= ((2q - 3z) - (q - 3z)) {}^{2} \\ = (2q - 3z - q + 3z) {}^{2} \\ = {q}^{2}$