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
