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2013-11-18T21:19:43-02:00
(10+3x)(10-3x)=10^2-(3x)^2=100-9x^2

(10+3x)(10-3x)=100-\not30x+\not30x-9x^2=\boxed{100-9x^2}
3 3 3
(10+3x).(10-3x)=10^2-(3x)^2=100-9x^2
(10+3x).(10-3x) = 10.10 -3x.10 +
(10 + 3x).(10 - 3x) > 10.10 - 3x.10 + 3x .10 -3x. +3x > 20 + 30x + 30x- 9x
> 20+60x + 9x > x=23/69 > x=3