Work Step by Step
Use the formula $(a+b)(a-b)$ to multiply the last 2 factors to obtain: $=(4x^2+9)[(2x)^2-3^2] \\=(4x^2+9)(4x^2-9)$ Use the same formula again with $a=4x^2$ and $b=9$ to obtain: $=(4x^2)^2-9^2 \\=16x^4-81$
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