Linear equations and inequalities of one variable 1. Let X / (a + B-C) = Y / (B + C-A) = Z / (a + C-B), find the value of (a-b) x + (B-C) y + (C-A) Z 2. Given / x + 5 / + / x-4 / = 9, find the value range of X (/ represents absolute value) 3. Cut two pieces of equal weight from two alloys of 7kg and 3kg respectively with different percentage of copper. Put the remaining part of each cut piece together with the rest of the other piece. After melting, the percentage of copper in the two alloys is equal. What is the weight of the cut alloy? 4. It is known that a, B and C are any real numbers, and it is proved that a ^ 2 + B ^ 2 + C ^ 2 > = AB + BC + ca 5. Given that x is a real number, prove 3 (1 + x ^ 2 + x ^ 4) > = (1 + X + x ^ 2) Only answer the third question, and don't answer the rest

Linear equations and inequalities of one variable 1. Let X / (a + B-C) = Y / (B + C-A) = Z / (a + C-B), find the value of (a-b) x + (B-C) y + (C-A) Z 2. Given / x + 5 / + / x-4 / = 9, find the value range of X (/ represents absolute value) 3. Cut two pieces of equal weight from two alloys of 7kg and 3kg respectively with different percentage of copper. Put the remaining part of each cut piece together with the rest of the other piece. After melting, the percentage of copper in the two alloys is equal. What is the weight of the cut alloy? 4. It is known that a, B and C are any real numbers, and it is proved that a ^ 2 + B ^ 2 + C ^ 2 > = AB + BC + ca 5. Given that x is a real number, prove 3 (1 + x ^ 2 + x ^ 4) > = (1 + X + x ^ 2) Only answer the third question, and don't answer the rest

4.a^2+b^2>=2ab
b^2+c^2>=2bc
a^2+c^2>=2ca
It can be superimposed in three ways