2. Sum and difference squared:
(a+b)2=a2+b2+2ab?
(a-b)2=a2+b2-2ab?
3. The cube of sum and difference:
a3+b3=(a+b)(a2-ab+b2)
a3-b3=(a-b)(a2+ab+b2)?
4, triangle inequality:
|a+b|≤|a|+|b|?
|a-b|≤|a|+|b|
| a |≤b & lt; = & gt-b≤a≤b?
5. Discrimination of roots
(1)b2-4ac=0 Note: The equation has two equal real roots.
(2)b2-4ac >0 Note: The equation has two unequal real roots.
(3)B2-4ac & lt; Note: The equation has no real root, but a complex number of the yoke.