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(6+9i)(6-9i) How to solve?

User Webeng
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1 Answer

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~~(6+9i)(6-9i)\\\\=6^2-(9i)^2~~~~~~~~~~~~~~~~~~~;[a^2-b^2 =(a+b)(a-b)]\\\\=36-81i^2\\\\=36-81(-1)~~~~~~~~~~~~~~~~;[i^2 = -1]\\\\=36+81\\\\=117

User DropAndTrap
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