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(4)
={(a-b)(a+b)}²(a²+b²)²
=(a²-b²)²(a²+b²)²
={(a²-b²)(a²+b²)}²
=(a⁴-b⁴)²
=a⁸-2a⁴b⁴+b⁸
(5)
=x(x-3)(x-1)(x-2)
=(x²-3x)(x²-3x+2)
=M(M+2)
=M²+2M
=(x²-3x)²+2(x²-3x)
=x⁴-6x³+9x²+2x²-6x
=x⁴-6x³+11x²-6x
(6)
=(x-2)(x+3)(x-4)(x+5)
=(x²+x-6)(x²+x-20)
=(M-6)(M-20)
=M²-26M+120
=(x²+x)²-26(x²+x)+120
=x⁴+2x³+x²-26x²-26x+120
=x⁴+2x³-25x²-26x+120