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)
