Q.1. Find a general formula for the number of match sticks used to make these patterns.

Dear Student,
The formula is :$Number of matches used=(n\times 5)-(n-1), Where n is the number of trapeziums$
So accordingly, When n=1, Number of matches used = 5(1)-(0)=5
When n=2,Number of matches=5(2)-(1)=9
When n=3,Number of matches=5(3)-2=13
When n=4,Number of matches=5(4)-3=17
When n=10,Number of matches=5(10)-4=46
When n=20,Number of matches=5(20)-19=81
When n=x,Number of matches= 5x-(x-1)= 4x+1
Regards