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What is the coefficient of the x^9y -term in the binomial expansion of (2y + 4x^3)4?

4
32
128
512

Question

Want a medal?
What is the coefficient of the x^9y -term in the binomial expansion of (2y + 4x^3)4?

4
32
128
512

anonymous · Answer

512$$256 x^{12}+512 x^9 y+384 x^6 y^2+128 x^3 y^3+16 y^4  $$

anonymous · Answer

@robtobey 
Um, I'm confused on how you got your answer. Could you explain, please?

anonymous · Answer

$$\left(4 x^3+2 y\right) \left(4 x^3+2 y\right) \left(4 x^3+2 y\right) \left(4 x^3+2 y\right) $$

anonymous · Answer

If you running on a Mac, use the Firefox browser, for viewing formulas.
Chrome is not rendering correctly on my machine.

anonymous · Answer

okay then what

anonymous · Answer

$$\left(4 x^3+2 y\right) \left(4 x^3+2 y\right)=16 x^6+16 x^3 y+4 y^2  $$$$\left(16 x^6+16 x^3 y+4 y^2\right) \left(16 x^6+16 x^3 y+4 y^2\right)= $$$$256 x^{12}+512 x^9 y+384 x^6 y^2+128 x^3 y^3+16 y^4  $$