Question

Solve for x in the equation x squared minus 4 x minus 9 = 29.
x = 2 plus-or-minus StartRoot 42 EndRoot
x = 2 plus-or-minus StartRoot 33 EndRoot
x = 2 plus-or-minus StartRoot 34 EndRoot
x = 4 plus-or-minus StartRoot 42 EndRoot

Answer 1

x^2 - 4x - 9 = 29
=> x^2 - 4x - 38 = 0

Use quadratic formula: x = [4 ± sqrt( (-4)^2 - 4(1)(-38) )]/2
= [4 ± sqrt(16 + 152)]/2
= [4 ± sqrt(168)]/2
= [4 ± 2√42]/2
= 2 ± √42.

So the correct choice is: x = 2 ± √42.