Find all roots of x2+4x−21x^2 + 4x - 21x2+4x−21.
x=3x = 3x=3 and x=−7x = -7x=−7
x=−3x = -3x=−3 and x=7x = 7x=7
x=1x = 1x=1 and x=−21x = -21x=−21
x=−1x = -1x=−1 and x=21x = 21x=21