а) (x - y)² - x² = ((x - y) - x) * ((x - y) + x) = (x - y - x) * (x - y + x) = -y * (2x - y) = y² - 2xy
б) b² - (a + b)² = (b - (a + b)) * (b + (a + b)) = (b - a - b) * (b + a + b) = -a * (a + 2b) = -a² - 2ab
в) (n + m)² - 16n² = ((n + m) - 4n) * ((n + m) + 4n) = (n + m - 4n) * (n + m + 4n)) = (m - 3n) * (m + 5n) = m² + 5mn - 3mn - 15n² = m² + 2mn - 15n²
г) 4c² - (k - 3c)² = (2c - (k - 3c)) * (2c + (k - 3c)) = (2c - k + 3c) * (2c + k - 3c) = (5c + k) * (k - c) = 5ck - 5c² + k² - ck = k² + 4ck - 5c²
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