Question

(a^2+b^2)(x^2+y^2
ره)
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Answer 1

$( {a}^{2} + {b}^{2} )( {x}^{2} + {y}^{2} ) \\ \\= a^2 (x^2+y^2)+b^2(x^2+y^2) \\\\ = {a}^{2} {x}^{2} + {b}^{2} {y}^{2} + {a}^{2} {y}^{2} + {b}^{2} {x}^{2}$

hope it helps.