28.比较下列两组数的大小. (1)2x2+x2x^{2}+x2x2+x与x2−1x^{2}-1x2−1; (2)2a2+2b22a^{2}+2b^{2}2a2+2b2与(a+b)2(a+b)^{2}(a+b)2.