Answer:
C 10
Explanation:
Heron's formula to calculate the area of a triangle based on 3 sides :
p (half the perimeter) = (a+b+c)/2
area = sqrt(p(p-a)(p-b)(p-c))
AB = c = sqrt(2² + 6²) = sqrt(40) = sqrt(4×10) = 2×sqrt(10)
AC = a = sqrt(2² + 4²) = sqrt(20) = sqrt(4×5) = 2×sqrt(5)
BC = b = sqrt(2² + 4²) = 2×sqrt(5)
p = 2×sqrt(5) + sqrt(10)
area = sqrt((2×sqrt(5) + sqrt(10))×sqrt(10)×sqrt(10)×(2×sqrt(5) - sqrt(10)) =
= sqrt(10×(2×sqrt(5) + sqrt(10))×(2×sqrt(5) - sqrt(10))) =
= sqrt(10×(4×5 - 10)) = sqrt(10×(20 - 10)) = sqrt(10×10) = 10