x^2 + ( m + n )x + m*n = ( x + m )( x + n ) ; We have m*n = 36 and m + n = b ; 1*36 = 36 ; m = 1 ; n = 36 ; the factors are ( x + 1 ) , ( x + 36 ) 2*18 = 36 ; m = 2 ; n = 18 ; the factors are ( x + 2 ) , ( x + 18 ) 3*12 = 36 ; m = 3 ; n = 12 ; the factors are ( x + 3 ) , ( x + 12 ) 4*9 = 36 ; m = 4 ; n = 9 ; the factors are ( x + 4 ) , ( x + 9 ) 6*6 = 36 ; m = 6 ; n = 6 ; the factors are ( x + 6 ) , ( x + 6 ) There are 5 pairs of number factors.