Using Pascal's triangle
Number of terms Expression
1 = 1----------------------------[tex](x+a)^0[/tex]
2 = 1 1----------------------------(x+a)
3 = 1 2 1-----------[tex](x+a)^2[/tex]
4= 1 3 3 1----------[tex](x+a)^3[/tex]
5= 1 4 6 4 1----------[tex](x+a)^4[/tex]
6= 1 5 10 10 5 1----------[tex](x+a)^5[/tex]
7= 1 6 15 20 15 6 1 ----------[tex](x+a)^6[/tex]
8= 1 7 21 35 35 21 7 1 ----------[tex](x+a)^7[/tex]
The meaning of [tex]_{3}^{6}\textrm{C}[/tex] , is coefficient of fourth term of an expression having 7 terms.
Using pascal Triangle value or coefficient of Fourth term of the expression
[tex](x+a)^6=\\\\\text{will be}\\\\_{3}^{6}\textrm{C}=20[/tex]
