If a$$\in$$R, b$$\in$$R, then the equation x² $$-$$ abx $$-$$ a² = 0 has

The solution of the inequality $${4^{ - x + 0.5}} - {7.2^{ - x}} < 4$$, x $$\in$$R is

Let x₁ and x₂ be the real roots of the equation $${x^2} - (k - 2)x + ({k^2} + 3k + 5) = 0$$, then maximum value of $$x_1^2 + x_2^2$$ is

When x¹⁰⁰ is divided by x² $$-$$ 3x + 2, the remainder is (2^{k + 1} $$-$$ 1)x $$-$$(2^k $$-$$ 1), then k is