X− + X− = X− + X−X− + X− = X− + X− B, 1 3 5 7A, 5 15 1990 19802015 2013 2011 20091990 1980 5 15HD
Bài 6, Tìm x, biết: x− + x− = x− + x−x− + x− = x− + x− b, 1 3 5 7a, 5 15 1990 19802015 2013 2011 20091990 1980 5 15HD: − + − = − + − x− x− x− x− 1 1 1 1a, => 5 15 1990 1980 1995 1995 1995 1995= + = += − = = =1995 0 1995x x = − + − = − + − b, 1 3 5 7− − − −2016 2016 2016 2016x x x x= + = + = − = = =2016 0 2016