The idea of factoring by grouping is to pull out something from each set of 2 terms so that what is left over inside the parenthesis is "like" between both factored sets. Like this: (x^5 - 3x^4) + (5x - 15). From the first set of parenthesis, pull out x^4 leaving (x - 3); from the second set pull out a 5 leaving (x - 3). So now what you have is this: x^4(x - 3) + 5(x - 3). Now factor out the
(x - 3): (x - 3)(x^4 + 5). There!