Given a ^ 2 + B ^ 2 + C ^ 2 = 1, x ^ 2 + y ^ 2 + C ^ 2 = 9, find the maximum value of AX + by + CZ The answer is 3

Given a ^ 2 + B ^ 2 + C ^ 2 = 1, x ^ 2 + y ^ 2 + C ^ 2 = 9, find the maximum value of AX + by + CZ The answer is 3

(a ^ 2 + B ^ 2 + C ^ 2) + 2m (AX + by + CZ) + m ^ 2 (x ^ 2 + y ^ 2 + C ^ 2) = (a + MX) ^ 2 + (B + my) ^ 2 + (c + MZ) ^ 2 > = 0. That is: for any m, 1 + 2 (AX + by + CZ) m + 9m ^ 2 > = 0 holds. So [2 (AX + by + CZ)] ^ 2-4 * 9