Tentukan daerah asal dari f(x) = x^2 + 2x + 1

fx - ( x² + 2 x 1 ) = x² + 2 + 1 - ( x² + 2 x + 1 )
fx - ( x² + 2 x + 1) = 0
( -1 ) x² + ( -1 ) × 2x - 1 + fx = 0
( -1 ) x² + ( -2 ) x - 1 + fx = 0
( -1 ) x² + ( -1 + f ) x - 1= 0
x ( f - 2 ) + ( -1 ) x2 - 1 = 0
( -1 ) x² + ( f -2 ) x - 1 = 0
x = - ( f - 2 ) + √( f - 2 )² - 4 ( -1 ) ( -1)   /2 ( -1 )
x = √ ( - 2 ) ² - 4 /2 + f /2 - 1, ≤ 0 atau f ≥ 4