How to replace one part of list of lists
Here are a few ways:
MapAt[Sqrt, data, {All, 1}]
Replace[data, {x_, y___} :> {Sqrt[x], y}, {1}]
data // Query[All, {1 -> Sqrt}]
SubsetMap[Sqrt, data, {All, 1}]
ReplacePart[data, {i_, 1} :> Sqrt[data[[i, 1]]]]
data2 = data;
data2[[All, 1]] = Sqrt[data2[[All, 1]]];
data2
☺ = {#^(1/2), ##2} &;
☺ @@@ data
{{7, 35, 14}, {8, 40, 16}, {9, 45, 18}}
or
☺☺ = {#^(1/2), ##2} & @@@ # &;
☺☺ @ data
{{7, 35, 14}, {8, 40, 16}, {9, 45, 18}}
What kglr posted, but a bit more "golfed"
data = {{49, 35, 14}, {64, 40, 16}, {81, 45, 18}};
{√#, ##2} & @@@ data
{{7, 35, 14}, {8, 40, 16}, {9, 45, 18}}