In a triangle with 2 sides given, The largest possible area is formed if these two sides are perpendicular to each other and also the two smaller sides among the 3 sides of a triangle. Care should be taken that the three sides so obtained do not violate the triangle principle.
1) Sum of two sides of a triangle must be greater than the third side.
2) Each side should be more than the difference between the other two sides.
Area would then be $1/2 * 7 * 8$ = $7*4$ = $28$
C