题目已知(x+y)2=4\left(x+y\right)^{2}=4(x+y)2=4,(x−y)2=16\left(x-y\right)^{2}=16(x−y)2=16,求下列各式的值:(1)x2+y2(1)x^{2}+y^{2}(1)x2+y2；(2)x4+y4(2)x^{4}+y^{4}(2)x4+y4.知识点：去括号与添括号章节：数与式 / 代数式
