To multiply \( 5\sqrt{15} \) and \( 4\sqrt{2} \), you can use the following steps:
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Multiply the coefficients (the numbers outside the square roots): \[ 5 \times 4 = 20 \]
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Multiply the square roots: \[ \sqrt{15} \times \sqrt{2} = \sqrt{30} \]
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Combine both results: \[ 5\sqrt{15} \times 4\sqrt{2} = 20\sqrt{30} \]
So, the final answer is: \[ 20\sqrt{30} \]