20.18!!!!!!!!!!!!!!!

1) х²(х+4) – 20х(х+4) + 100(х+4) = = (х+4)(х² – 20х + 100) = = (х+4)(х – 10)² 2) а² – 36 – 2а(36 – а²) – а²(36 – а²) = = (а² – 36) + 2а(а² – 36) + а²(а² – 36) = = (а² – 36)(1 + 2а + а²) = = (а² – 36)(1+а)² 3) а²(b-1) – b²(a-1) = = a²b – a² – ab² + b² = = (a²b – ab²) - (a² – b²) = = ab(a – b) – (a – b)(a+b) = = (a – b)(ab – a – b) 4) (m-n)(n³-p³) – (n-p)(m³ – n³) = = (m - n)(n - p)(n²+ np + p²) – (n-p)(m – n)(m² + mn + n²) = = (m - n)(n - p)((n²+ np + p²) –(m² + mn + n²)) = = (m - n)(n - p)((n²+ np + p² –m² - mn - n²)  

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