a^3-b^3=(a-b)(a^2+b^2+ab)
=(a-b)b
Х^2-14х-72 = 0
По теореме Виетта:
х1+х2 = 14
х1*х2 = -72
х1 = 18
х2 = -4
1) 7x(3x-2)+(x-4)(x+4) = 21x² - 14x + x² - 4² = 22x² - 14x - 16;
2) (y-4)(y-6)+(y+5)² = y² -6y - 4y + 24 + y² + 10y + 25 = 2y + 49;
3) 4(x-8)²-4x² = 4(x² - 16x + 64) - 4x² = 4x² - 64x + 256 - 4x² = -64x + 256;
4) 4x(2x-1) + (x-3)(x+3) = 8x² - 4x + x² - 3² = 9x² - 4x + 9;
5) (p-3)(p-11) + (p+6)² = p² - 11p - 3p + 33 + p² + 12p + 36 = 2p² - 2p + 69;
6) 7(a+b)² - 14ab = 7(a²+2ab+b²) - 14ab = 7a² + 14ab + 7b² - 14ab = 7a² + 7b².