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# How do you know which method to use to solve quadratic equations? watch

1. how do you know whether to factorise it, complete the square, use the quadratic formulae ect?
2. (Original post by Bertybassett)
how do you know whether to factorise it, complete the square, use the quadratic formulae ect?
You can use any method unless the question specifies otherwise.
Always factorise if you can. It is likely to be the most efficient method. Make sure you have a method to factorise trickier problems where the coefficient of x squared is greater than 1.
If it doesn't factorise or you can't see how it does or you are told the solutions will be in some kind of surd form or it says "exact solutions" then you can use either the formula or completing the square. They are effectively the same thing. Most people find it easier and more efficient to memorise the formula than follow the completed square process.
Some questions will ask you to write a quadratic in completed square format. They may then say "hence solve" in which case they want you use the completed square or the may say "hence or otherwise" in which case it's up to you.
On a calculator exam if you are told to give your answer to "3 significant figures" this tells you it doesn't factorise and the formula is probably the best approach.

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