Hi! I was doing this problem on the one month plan and was wondering my way ( blue) was incorrect.
Incorrect, Red is correct way.
Square_root function is not additive i.e. the square root of a sum cannot be simplified by taking the square root of each term and adding them together. (That’s why your blue solution is wrong)
eg: https://proofwiki.org/wiki/Additive_Function_(Conventional)/Examples/Square_Root_is_not_Additive