4x²-17x-42 by factor

4x²-17x-42

=4 (x²-17/4x) - 42

=4[x²-17/4 x + (-17/8) ² - (-17/8) ²]-42

=4 (x-17/8) ²-289/64-42

=4 (x-17/8) ² - (289+2688) / 64

=4 (x-17/8) ²-2974/64

=[ (2x-34/8) ² - (√2974/8) ²]

= (2x-34/8 + (√2974/8)) (2x-34/8 - (√2974/8)

=[2x + (√2974-34) / 8][2x - (√2974+34) / 8]