We will identify the longest side, c (integer value here) for such problems.
It is c=7, and the other two sides can slide from LHS and RHS towards each other.
The options include c= {7, 6, 5, 4, 3, 2, 1}. Other two sides slide in line with triangle properties and perimeter constraint: a+b+c=15, a-b<c<a+b
c=7, a+b=8 (options a-b are flexible)
c=6, a+b=9
...
c=1, a+b=14 (a=b=7)
Shortcut is to identify the longest possible side and set this as the number of triangles sought by similar problem.
KarunMendiratta wrote:
How many triangles with perimeter 15 can be formed such that all three sides are integer?
A. 7
B. 6
C. 8
D. 5
E. 4