... (1) Li cú: a - b = d x - y > d , Suy a - b > 3ab 2) Tìm tất cặp số nguyên (x; y) thoả mãn phng trỡnh: x2 + y2 = 3x + xy ã Nhõn v vi cú (2 x - y - 3) + 3( y - 1) = 12 Ta cú ( 2x y -3 )2 l s chớnh ... 1) = P(P(x)+x) vi mi x ã Chn x = 2015, x= 2016 cú: ã P (2015) .P(2016) P( P (2015) + 2015) P (2015) = = P(2017).P (2016) P( P(2016) + 2016) P(2017) ã Vy m = 2015 + P (2015) v n = 2016 + P(2016) tha ... trỡnh : ỡ2 x + x = y + y,(1) ù 2 ù x - y = -1 (2) ợ ã Thay = - x + y vo PT(1) cú : ( x - y )(( x + Suy x = y hoc x = y =0 ã Thay y = x vo PT(2) cú x = 1, x = -1 ã Nghim ca h x = y = Cau III:2,5...