Question

разложите на множители
$(a - 2)^{2} + 4(a - 2) - 21$

Answer 1

$(a - 2) {}^{2} + 7(a - 2) - 3(a - 2) - 21 = \\ \\ (a - 2)(a - 2 + 7) - 3( a - 2 + 7) = \\ \\ (a - 2 + 7)(a - 2 - 3) = \\ \\ (a + 5)(a - 5)$

Answer 2

$x^2+4x-21=0\; \; \to \; \; x_1=-7\; ,\; x_2=3\; \; (teorema\; Vieta)\; \; \Rightarrow \\\\x^2+4x-21=(x+7)(x-3)\; \; \; \Rightarrow \\\\x=(a-2)\, :\; (a-2)^2+4(a-2)-21=(a-2+7)(a-2-3)=(a+5)(a-5)$