First factor like terms
4x³ + 8x² - 25x - 50
4x²(x + 2) - 25(x + 2)
See that the factor in parenthesis is the same? Because they are the same, you can pair the outside factors together in a parenthesis.
(4x² - 25)(x+2)
factor (4x² - 25) = (2x + 5)(2x - 5)
= (2x - 5)(2x + 5)(x + 2)