In one study on the effect of tea tree oil on acne, 65 subjects were chosen randomly to use tea tree oil and 65 were chosen to use a placebo. In a second study, 165 subjects who acknowledged being long-time tea tree oil users had their acne compared with those of 165 people who had never used tea tree
oil. Identify the types of studies performed.

Both studies were controlled experiments.

Both studies were observational studies.

Each study was part controlled experiment and part observational study.

The first study was an observational study whereas the second was a controlled experiment.

The first study was a controlled experiment whereas the second was an observational study.

25.2

step-by-step explanation:

2+4x6-8/10= 25.2

the answer would be d.

step-by-step explanation:

move all variables to the left side and all constants to the right side

(x−3)^2+(y−1)^2=16

this is the form of a circle. use this form to determine the center and radius of the circle.

( x − h ) 2 + ( y − k ) 2 = r 2

match the values in this circle to those of the standard form. the variable   r   represents the radius of the circle,   h   represents the x-offset from the origin, and   k   represents the y-offset from origin.

r = 4

h = 3

k = 1

the center of the circle is found at   ( h , k ) .

center:   ( 3 , 1 )

these values represent the important values for graphing and analyzing a circle.

center:   ( 3 , 1 ).

radius:   4