(a)
We have been given an equation  . Upon taking derivative of this equation with respect to x on both the sides, we get:
. Upon taking derivative of this equation with respect to x on both the sides, we get:

(b)
In order to write the equation of tangent line, we need to find the slope of the line. We know that point (3,11) lies on the graph. Therefore, we write the slope of the tangent as:

Therefore, equation of tangent line is:

(c)
We know that slope of tangent is given as  . The tangent will be vertical when denominator of slope is zero, that is:
. The tangent will be vertical when denominator of slope is zero, that is:

 
        
             
        
        
        
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Answer:
a. longitudinal 
Explanation:
A longitudinal study examines a given group over a long period of time, so collecting data from the same group of 30 people over their lifetime certainly fits that definition.  It's more like an evolution study.
A cross-sectional compares different groups at the same point in time.  So, it's more like a survey.
A microgenetic is much focused in time, providing multiple data sets in a short time to examine rapid evolution of a subject.
An experimental study design will make interactions and experiments with the study group, while this is not the case here apparently, and experimental is usually for a much shorter period than a generation.
 
        
             
        
        
        
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hope this helps, good luck! :)
        
             
        
        
        
<span>B)<span>employees should be hired according to overall intelligence</span></span>