Ab - 0.5b when a = 1 and b = 5

2.5

Step-by-step explanation:

a = 1

b = 5

ab

= 1 x 5

= 5

0.5b

= 0.5 x 5

= 2.5

ab - 0.5b

= 5 - 2.5

= 2.5

2.5

Step-by-step explanation:

ab - 0.5b

a = 1 and b = 5

(1)(5) - 0.5(5)

Multiply (1)(5) = 5

5 - 0.5(5)

Multiply -0.5(5) = -2.5

5 - 2.5

Subtract 5 - 2.5 = 2.5

2.5

there are lots of ways.   pick's theorem tells us if the vertices are lattice points the area a is

a = b/2 + i - 1

where b is the number of boundary lattice points and i is the number of interior lattice points.

in the figure i count b=16, i=50 so

a = 8 + 50 - 1 = 57

let's try the shoelace formula.   the area is half the sum of the cross products of the sides.  

a(-2,6)   -2(2)-6(-5) = 26

b(-5,2)   -5(-3) - 2(-2) = 19

c(-2,-3) -2(-3) - (-3)(4) = 18

d(4,-3)   4(3) - (-3)(5) = 27

e(5,3)   5(3) - 3(1) = 12

f(1,3)     1(6) - 3(-2) = 12

a(-2,6)

each of the cross products is twice the area of the triangle with the associated side and one vertex the origin. so the area of abo=26/2=13.

area = (1/2) (26 + 19 +   18 + 27 + 12 + 12) = 57

that checks!