5) \(\left(x-3\right)\left(x+5\right)-\left(x-2\right)\left(x+2\right)\)
\(=\left(x^2+5x-3x-15\right)-\left(x^2-4\right)\)
\(=\left(x^2+2x-15\right)-\left(x^2-4\right)\)
\(=x^2+2x-15-x^2+4\)
\(=2x-11\)
6) \(\left(\dfrac{1}{4}x-y\right)\left(x^2+4xy+16y^2\right)+4\left(4y^3-\dfrac{1}{16}x^3+1\right)\)
\(=\left(\dfrac{1}{4}x\right)^3-y^3+16y^3-\dfrac{1}{4}x^3+4\)
\(=\dfrac{1}{64}x^3-y^3+16y^3-\dfrac{1}{4}x^3+4\)
\(=-\dfrac{15}{64}x^3+15y^3+4\)
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