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a²-4 = a² -2² = (a-2)*(a+2)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
a²-6a+8 = 0
D = (-6)² - 4 * 8 = 36 - 32 = 4 = 2²
a²-6a+8 = (a-4)*(a-2)
____________________________
a²-4 = a² -2² = (a-2)*(a+2)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
a²-6a+8 = 0
D = (-6)² - 4 * 8 = 36 - 32 = 4 = 2²
a²-6a+8 = (a-4)*(a-2)
____________________________