由完全平方式(a-t)2≥0易得如下的:命题a2≥2at-t2,其中t为参数.此不等式有着很好的应用价值,我们以一些竞赛题为例来加以说明.例1(前苏联奥尔德荣尼基市第三届数学竞赛题)已知x,y,z∈R+,且x+y+z=1,则x2+y2+z2≥13.证明由命题有:x2≥2tx-t2,y2≥2ty-t2,z2≥2tz-t2,三式相加得:x By the completely flat method (at) 2 ≥ 0 is easy to get the following: Proposition a2 ≥ 2at-t2, where t is a parameter. This inequality has a very good application value, we use some contest titles as an example to illustrate. Example 1 ( The third mathematics contest of the former Soviet Union, Alde Jonigi, known for x, y, z∈R+, and x+y+z=1, then x2+y2+z2≥13. Prove that the proposition has: x2 ≥ 2tx-t2, y2≥2ty-t2, z2≥2tz-t2, Addition of three formulas: x