1. the radioisotope iodine-123 is used in thyroid therapy. the half-life of this isotope is 13.27 hours. which equation determines the percent of an initial amount of the isotope remaining after t hours? a = 13.27 (1/2)^100/t a = 100 (1/2)^13.27/t a = 13.27 (1/2)^t/100 a = 100 (1/2)^t/13.27 2. a ladder leans against a building. the foot of the ladder is 2 feet from the building and reaches to a point 7 feet high on the building. what is the measure of the angle formed by the ladder and the building? enter your answer, rounded to the nearest degree, in the box.

1. D. A = 100 (1/2)^t/13.27

Exponent equation formula would be an= a0( 1+r)^t
In this question, the radio isotopes will become half of its weight after the half-life. So, the ratio would be -0.5 (r= -0.5)
The halftime is 13.27 hours, so the time will be divided by that number. The result would look like this:
an= a0( 1+r)^t
an= a0( 1-0.5)^t/13.27
an= a0( 1/2)^t/13.27

2. x= 74°

The ladder and the building will make a right triangle with the ladder as the hypotenuse. 
The foot of the ladder is 2 feet from the building, so the adjacent side is 2ft.
It reaches a point 7 feet high on the building, so the opposite side is 7ft
You can find the angle by using the tan equation

tan x= opposite / adjacent
tan x= 7/2= 3.5
x= 74°