PLZ HELPP Which system of equations has exactly one solution?

O 2x-4y=8
x+y= 7

O 3x+y=-1
6x+2y =-2

O 3x+3y = 3
-6x-6y = 3

O 3x-2y = 4
-3x+2y = 4

What is the name used to describe a graph where for some value of x, there exists 2 or more different values of y?

What is the axis of symmetry of the function f(x)=-(x+ 9)(x-21)

Two researchers are attempting to create a new psychotherapy protocol that more reduces panic attacks. they believe that they have succeeded and are now in the clinical trial period of their protocol's development. they are working with several cohort groups, some of which have been through the new protocol, while others have done the standard protocol currently recommended. if these researchers are interested in evaluating the difference in the percentage of test subjects who successfully decreased their panic attacks in 2 months on the new protocol versus the percentage of test subjects who successfully decreased their panic attacks in 2 months with the traditional protocol, which of the following statistical tests would be most appropriate? a. analysis of variance (anova) b. correlation c. chi-square test d. paired t-test e. independent t-test