idiom "to fighting mad"

[oboeteru]

What surprised me is -ing form after to. :shock:
Is it correct to use verbs that finish with -ing this way? Why isn't it just to fight mad? Kind of exception or what? If it's common use, could you explain me when I can use it this way?
On the other hand I found it in one of internet dictionaries so I suppose there can be a few mistakes.

And one more phrase I have hard time with:
I haven't filled in my tax return yet and I don't how to work out my net profits.

For me the underlined part lacks of know (I don't know how to work out...). However, my head becomes completely dizzy about such things so I prefer to ask here

 

[5jj]

What surprised me is -ing form after to. :shock:
Is it correct to use verbs that finish with -ing this way? Why isn't it just to fight mad? Kind of exception or what? If it's common use, could you explain me when I can use it this way?

If you can provide the whole sentence from which these words were taken, we may be able to offer an explanation.

I haven't filled in my tax return yet and I don't know how to work out my net profits.

You are right: 'know' is missing.

 

[oboeteru]

thanks for answer

The problem is that there was no exact sentence, I mean, in the definition that is given usually as basic form of the verb it was put exactly: to fighting mad.
About the example I don't see anything wrong about it, it's: If Jerry finds out you've driven his car, he'll be fighting mad. Just first conditional.

 

[5jj]

I suggest you use a different dictionary in future.

 

[oboeteru]

I take your answer as it should be "to fight mad", then
Thx for dispelling my doubts!

 

[5jj]

The idiom is [STRIKE]to[/STRIKE] fighting mad; 'fighting' functions as an adverb.

You are fighting mad, extremely mad, etc; you don't fight mad.