I will agree with mm but only if the cable joiner will be dragging through damp wet grass hence why I say cut the machine cable back.
Look these up enter cable joiners in search engine see the article you then know what to use/buy/beg/steal or borrow and forget to take back.
1. Twin pin and socket cable joiner
2. OR a three pin one if it requires earth.
3. determine the loss of length if you cut back the cable on the machine to within 12inches of where it enters the machine. If too much lost think new cable for the MAINS side.
Connect the SOCKET side of the cable connector to the MAINS lead. and the PIN side to the machine. Having cable a foot long at machine end keeps it out of damp grass etc.
2. Price up cost of replacing the cable.
I've just put a plug and socket cable joiner on my B&D strimmer after being fed up untangling the cable.
Bob
September 2012