1.) use the quadratic formula to solve the equation. if necessary, round to the nearest hundredth .x squared minus 21 x equals negative 4 x 2.) which kind of function best models the data in the table? use differences or ratios. x y 0 1.7 1 6.8 2 27.2 3 108.8 4 435.2 3.) solve the system of equations algebraically. show all of your steps. y equals x squared plus two x; y equals three x plus twenty !

Part 1
We are given . This can be rewritten as .
Therefore, a=1, b=-18, c=0.
Using the quadratic formula
     
     

The values of x are
     
     

Part 2
Since the values of y change drastically for every equal interval of x, the function cannot be linear. Therefore, the kind of function that best suits the given pairs is a quadratic function. 

Part 3.
The first equation is .
The second equation is .

We have 
     
     
Factoring, we have 
     
Equating both factors to zero.
     
     

When the value of x is 6, the value of y is 
     

When the value of x is -3, the value of y is 
     

Therefore, the solutions are (6,38) or (-3,11)