If a, B and C are real numbers which are not equal to each other and satisfy the relation B2 + C2 = 2A2 + 16A + 14 and BC = a2-4a-5, then the value range of a is______ ．

If a, B and C are real numbers which are not equal to each other and satisfy the relation B2 + C2 = 2A2 + 16A + 14 and BC = a2-4a-5, then the value range of a is______ ．

∵ B2 + C2 = 2A2 + 16A + 14, BC = a2-4a-5, ∵ (B + C) 2 = 2A2 + 16A + 14 + 2 (a2-4a-5) = 4a2 + 8A + 4 = 4 (a + 1) 2, that is, there is B + C = ± 2 (a + 1) and BC = a2-4a-5, so B and C can be regarded as two unequal real roots of the univariate quadratic equation x2 ± 2 (a + 1) x + a2-4a-5 = 0, so △ = 4 (...)

If one root of the equation x2 + MX + n = 0 is zero and the other root is nonzero, then the value of M, n is ()
A. m=0，n=0B. m=0，n≠0C. m≠0，n=0D. mn≠0

Let this nonzero root be α, then α· 0 = n = 0, α + 0 = - M ≠ 0, so C is chosen

Each pair of little rabbits grows into big rabbits one month after birth, and each pair of big rabbits can produce a pair of little rabbits every month. If a person buys a pair of little rabbits in January, how many pairs of rabbits does he have in December?

The number of rabbits in each month is the number of rabbits in last month, and the number of rabbits in each month is the number of rabbits in last month, that is, the number of rabbits in last month, so the number of rabbits in each month is the sum of the number of rabbits in last month and the number of rabbits in last month