Question 461705
the area of the triangle with vertices 

A(-1,3)

B(2,3)

C(2,6)

first find a distance between vertices which is equal to the length of sides:

a distance between vertices 
A(-1,3)
B(2,3) 

is: 

*[invoke Distance_Formula_for_Coordinate_Plane -1, 3, 2, 3]

so, {{{AB=c=3}}}

a distance between vertices 
A(-1,3)
C(2,6)

is: 

*[invoke Distance_Formula_for_Coordinate_Plane -1, 3, 2, 6]

so, {{{AC=b=4.24}}}

a distance between vertices 
B(2,3) 
C(2,6)

is: 

*[invoke Distance_Formula_for_Coordinate_Plane 2, 3, 2, 6]

so, {{{BC=a=3}}}


*[invoke heros_formula 3, 4.24, 3]