Dear Friends
Being new to Libre Office in General I am using writer to help create notes inserting formulas using libre office math.
I am typing up worked examples and would like to underline with an arrow head at the end my answer.
For example if my answer =2 cos 2x
I would like that to have an underline and and arrow head the best I can find after googling and so on is the command “underline”
Any suggestions?
Thank you
Godfrey Hamshire
Your help and suggestions
Do you need an arrow pointing to an underlined answer or the answer to be underlined by an arrow? The first is relatively easy, for the second you need to be “creative” 
"Answer" rightarrow underline{ 2 cos 2x }
newline
"Answer" rightarrow color red { underline{ color black { 2 cos 2x } } }
newline
"Answer" rightarrow {2 cos 2x} csub{ "―――――▶" }
Notice that the “arrow” on the last line was built using several m-dashes and a “triangle”. To insert them on Math you can either copy paste them from Writer or use their unicode codes, remembering that since 5.2 (I think) you can switch between unicode codes and the character with the keyboard shortcut Ctrl X:
m-dash: U+2015 ―
Triangle: U+25b6 
Thank you very much for your help and suggestions
Best wishes
Godfrey