Question 499772
{{{sqrt(5x) = sqrt(5) * sqrt(x)}}}
{{{sqrt(3x) = sqrt(3) * sqrt(x)}}}
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substitute
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{{{sqrt(5x) + sqrt(3x) = sqrt(5) * sqrt(x)  + sqrt(3) * sqrt(x)}}}
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which can be simplified to be
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{{{(sqrt(5) + sqrt(3)) * sqrt(x)}}}
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Done.