(urgent) x, y and Z are real numbers which are not all zero. The denominator is the square of X + the square of Y + the square of Z, and the numerator is XY + 2yz Function part It's all wrong. It's different from the answers at the back of the book.

(urgent) x, y and Z are real numbers which are not all zero. The denominator is the square of X + the square of Y + the square of Z, and the numerator is XY + 2yz Function part It's all wrong. It's different from the answers at the back of the book.

Let the original formula ≤ 1 / a (a > 0) be constant. This inequality can be reduced to x ^ 2 + y ^ 2 + Z ^ 2-ax-2ayz ≥ 0, that is, (X-ay / 2) ^ 2 + (z-ay) ^ 2 + (1-5a ^ 2 / 4) y ^ 2 ≥ 0. Since x, y and Z are not all 0, then (X-ay / 2) ^ 2 + (z-ay) ^ 2 > 0 and can infinitely tend to 0, so 1-5a ^ 2 / 4 ≥ 0, then there is a ≤ 2 / sqrt (5), so the original formula ≤