Give an expansion like (a + b)n
(a + b)2 = a2 + 2ab + b2
(a + b)3 = a3 + 3a2b + 3ab2 + b3
(a + b)4 = a4 + 4a3b + 6a2b2 + 6ab3 + b4
To divide sth into two equal parts.
Having two variables.
An agreement by a government or a company to pay you interest on the money you have lent.
bound, boundary 边界，界限；线
- A real or imagined line that marks the limits or edges of sth and separates it from other things or places.
- The collection of all points of a given set having the property that every neighborhood of each point contains points in the set and in the complement of the set.
The measure or dimension from side to side; width.