How do you simplify #sqrt( 8 x + 1) = 5#?
#color(blue)(sqrt( 8 x + 1) = 5#
Square both sides to get rid of the radical sign
Square root is an 'action'. To 'get rid' of that action you reverse it!
The reverse of square root is to square it.
Square both sides giving:
Subtract 1 from both sides (the revers of add is subtract)
Divide both sides by 8 (the reverse of multiply is divide).