Factor the polynomial x2 + x - 6. which one of the following is a factor?

 I do a couple of them so you can get an idea how to do the rest: 

15) x2 - 18x + 80. 

x^2 - 18x + 80 
(x - 8)(x - 10) 

17) Solve the given equation by using the quadratic formula. 

x2 - 7x - 4 = 0 
ax² + bx + c = 0 
x = [- b ± √(b² - 4ac)] / 2a 
in this case: a = 1 , b = - 7, c = - 4 
plug in and solve for x. 
x = [ 7 ± √(49 + 16)] / 2 
x = ( 7 ± √65) /2 
x = ( 7 ± 8.06) / 2 
x = - 0.53, 7.53 

The value under square root is 65. 

20) Find the vertex of the parabola y = x2 - 4x 
vertex >> x = - b/2a = 4/2 = 2 
y = 2^2 - 4(2) = 4 - 8 = - 4 

vertex is at: (2, - 4)