Explanation:
Actually, it isn't that hard. Remember the difference of squares? (a + b)(a - b) = a² - b² and in this case 9 is a and 4x is b so our answer is 81 - 16x².
Answer:
9 - 16x²
(3+4x)(3-4x)= 3²- (4x)²= 9 - 16x²
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