А6 = а1 + 5d = 2 + 5·(-3) = 2 - 15 = -13
S6 = (2 -13)·6/2 = -11·3 = -33
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А)125a³-8b³ = (5а)³ - (2b)³ = (5а-2b)((5а)²+5a·2b+(2b)²) =
= (5а-2b)(25а²+10ab+4b²)
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б) a</span>³+27b³ = (а)³ + (3b)³ = (а+3b)(а²-a·3b+(3b)²) =
= (а+3b)(а²-3ab+9b²)
<span>
в) x</span>⁶-a⁶ = (x²)³ - (a²)³ = (x²-a²)((x²)²+x²·a²+(a²)²) =
= (x-a)(x+a)(x⁴+a²x²+a⁴)