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 5i√3

i is the square root of -1. Factor that out, along with 5, the square root of 25. That leaves 3 inside the radical.

Step-by-step explanation:  

Separate the factors of the number inside the radical, look for perfect squares:

If the number is negative, factor -1, and use i as the imaginary square root of negative 1. and move that out to the left of the radical.

If there is a perfect square, take the square root and move that out to the left of the i outside the radical.

Leave any other values inside the radical.