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Question
Compute the indicated products:
`[[a b],[-b a]][[a -b],[b a]]`
Solution
`[[a b],[-b a]][[a -b],[b a]]`
`⇒ [[a xx axx+b+b axx(-b)+bxxa],[(-b)xxa+axxb (-b)xx(-b)+axxa]]`
`⇒[[a^2+b^2 -ab^2+ab],[-ab+ab b^2+a^2]]`
`⇒[[a^2+b^2 0],[0 a^2+b^2]]`
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