{x4+y4=1(1)x6+y6=1(2) pt(1) => x,y thuoc [-1;1] (2)-(1) <=>x^4 (x^2 -1) + y^4(y^2-1) = 0 (3)
do x,y thuoc [-1;1] =>x^2 - 1 < hoac = 0.y^2 < hoac = 0
(3) dung <=> x^4 (x^2 - 1) = 0 va y^4(y^2 - 1) = 0(ta tim dk nghiem roi thu lai pt (1))
. giai ra ta duoc cac nghiem (1;0);(-1;0);(0;1);(0;-1)