multiplying polynomials: (9c - 4d)(9c + 4d)

[zhyia]

(9c - 4d) (9c + 4d)

= 81c^2 + 16d^2

(7a - 2b)(2a + 4b)

= 14a^2 + 32ab - 4ab - 8b^2

= 14a^2 + 28ab - 8b^2

 

[steve_b]

(9c-4d) (9c+4d)

=81c^2+16d^2

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Make that : 81c^2 - 16d^2

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(7a-2b)(2a+4b)

14a^2+32ab-4ab-8b^2
=14a^2+28ab-8b^2

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Almost...

14a^2 + 28ab - 4ab - 8b^2

14a^2 + 24ab - 8b^2

Steve