题目已知(x+y)2=7\left(x+y\right)^{2}=7(x+y)2=7,(x−y)2=3\left(x-y\right)^{2}=3(x−y)2=3,求x2+y2x^{2}+y^{2}x2+y2的值.知识点：去括号与添括号章节：数与式 / 代数式
