3a + 5 - (10-2a) = 3a + 5 - 10 + 2a = 5a - 5(1)当5a - 5 = 0,也就是a=1时有3a + 5 - (10-2a) = 5a - 5 = 0也就是3a + 5 = 10 - 2a(2) 当5a-5>0,也就是a>1时有3a + 5 - (10-2a) = 5a - 5 > 0也就是3a+5 > 10-2a(3)...