a) $(1.2x-4)(1.2x+4) - (1.3x-2)(1.3x+2) = 0.5x(8-0.5x) \Rightarrow 1.44x^2 - 16 - (1.69x^2 - 4) = 4x - 0.25x^2 \Rightarrow 1.44x^2 - 16 - 1.69x^2 + 4 = 4x - 0.25x^2 \Rightarrow -0.25x^2 - 12 = 4x - 0.25x^2 \Rightarrow -12 = 4x \Rightarrow x = -3$
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