economic/economical
economic (1) = connected with the economy
The article deals with the government's economic policy.
economic (2) = producing enough profit; profitable
The factory is no longer economic, so they will have to shut it down.
economical (1) = providing good service in relation to the amount of money spent
My new car is highly economical - it uses only four litres of petrol per 100 kilometres.
economical (2) = careful about spending money; thrifty
John is economical in all areas of life.
historic/historical
historic = important in history; likely to be remembered (e.g., a building, occasion, day, victory...)
The two countries are about to make a historic agreement.
historical (1) = really existing in history
Was Robin Hood a historical figure? (= a real person)
historical (2) = connected with the study of history (e.g., documents, records, research...)
Martin is doing historical research into the First World War.
Note also the difference between the following phrases:
history book = a non-fiction book about great achievements in history
historical novel = a novel about people and events in the past
classic/classical
classic (1) = accepted by most people as one of the best of its kind (e.g., a movie, author, work...)
It's a classic 1960's novel.
classic (2) = a typical example of something
Mike made a classic mistake in the exam - he wrote "she like..." instead of "she likes..."
classic (3) = traditional in style or design; elegant (e.g., a car, suit, furniture...)
Pete was wearing a classic grey suit.
classical (1) = connected with the culture of ancient Greece and Rome
Maria studies classical languages and literature. (= Greek and Latin)
classical (2) = classic (2)
This is a classical example of bad behaviour.
classical (3) (of music) = not played on electronic instruments (not pop or jazz); serious
My dad prefers classical music to pop.
comic/comical
comic (1) = connected with comedy
We saw a comic opera last weekend.
comic (2) = funny in a theatrical way
There are a lot of comic scenes in the book.
comical (a rather old-fashioned word) = funny or amusing because of being unusual
She had a comical expression on her face.
electric/electrical
electric (1) = used with the names of particular machines which produce or use electricity, e.g., motor, light, guitar, etc.
Every hospital has to have its own electric generator.
electric (2) = full of excitement
The atmosphere at the party was electric.
electrical = used with more general words connected with electricity, e.g., appliance, equipment, component, etc.
My brother studies electrical engineering.
politic/political
politic = based on good judgements; wise
It doesn't seem politic to ask them for any more money now.
political = connected with politics
I think listening to political debates is a waste of time.
magic/magical
magic = having or using special powers; used especially in fixed expressions such as a magic carpet/spell/trick/wand, etc.
Look, I'll show you a new magic trick.
magical = used especially in metaphorical senses in the meaning of "mysterious", "wonderful" or "exciting"
The trip was a magical experience.
music/musical
music = connected with music (used in noun compounds), e.g., music business/industry/lessons
Uncle Mark works in the music industry.
musical = connected with music; containing music (used as an adjective), e.g., musical talent/production/instrument
Can you play any musical instruments?
problem/problematic/problematical
problem = causing problems
Their youngest son is a problem child. He's so naughty.
problematic/problematical = difficult to deal with; full of problems
We got into a problematic situation.
As you can see, the "-ic/-ical words" are pretty problematic(al) to use correctly, but there is no need for you to avoid them. Always bear in mind that nobody's perfect and to err is human, so don't be afraid to take some risks when using English.