The first part is to prove the sufficiency (forward push), and the second part is to prove the necessity (backward push), thus proving that m is a necessary and sufficient condition for n, and ordinary beginners will find the answer confusing or verbose. Also: the expression of the answer is really not clear enough. Can you put x? Change it to t and the equation becomes t? +pt+p- 1=0, (t>0) This may be better understood!