<s>[INST] Pre calculus fraction simplify question Simplify:
$$\frac{\frac{16x^4}{81} - y^4}{\frac{2x}{3} + y}$$
Wolfram alpha confirms the answer from the answer sheet: Wolframalpha answer
 [/INST] Multiplying by 81 on the top and the bottom gives
$\displaystyle\frac{16x^4-81y^4}{27(2x+3y)}=\frac{(4x^2-9y^2)(4x^2+9y^2)}{27(2x+3y)}=\frac{(2x-3y)(2x+3y)(4x^2+9y^2)}{27(2x+3y)}=$
$\frac{1}{27}(2x-3y)(4x^2+9y^2)$.
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