I. Basic inequality
√(ab)≤(a+b)/2, then it can be changed into the square of the average value of a 2-2ab+b 2 ≥ 0, a 2+b 2 ≥ 2ab, AB≤A and B.
Second, the absolute inequality formula
| |a|-|b| |≤|a-b|≤|a|+|b| .
| |a|-|b| |≤|a+b|≤|a|+|b| .
Third, Cauchy inequality.
Let a 1, a2, an, b 1, b2 and bn all be real numbers, then (a1b1+a2b2+anbn) 2 ≤ (a12+a22+an2) *.
Fourthly, triangle inequality.
For the reinforced inequality of any two vectors b, this inequality can also be called the triangular inequality of vectors.
Five, quadrilateral inequality
If for any a 1 ≤ a2