Because this is a right angle, we could use the pythagorean theorems. Knowing that the area of a triangle equals half of the base multiplied with the height, we have to determine first the two other legs.
Find BC (height):
cos 45° = BC/24
BC = 16.97 ft
Find AC (base):
sin 45° = AC/24
AC = 16.97 ft
Then,
A = 1/2*16.97*16.97
A = 144 ft^2
