Question 329753
(2s + 5z)^2 (s + 3z)^2 
This is what I get: 
= (2s + 5z) (2s + 5z) (s + 3z) ²
= 4s² + 10sz + 10sz + 25z² (s + 3z) (s + 3z)
= 4s² + 10sz + 10sz + 25z² + s² + 3sz + 3sz + 9z²
= 4s² + s² + 10sz + 10sz + 3sz + 3sz + 25z² + 9z²
= 5s² + 26sz + 34z² 
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Why did you add them?
{{{(2s + 5z)^2 (s + 3z)^2}}}
= {{{(4s^2 + 20sz + 25z^2)*(s^2 + 6sz + 9z^2)}}}
= {{{4s^4 + 44s^3z + 181s^2z^2 + 330sz^3 + 225z^4}}}