i am so confused (gcse maths)
when can i use the quadratic formula in maths and when do i have to work it out not using the quadratic formula?
Original post by amelia.c.r
when can i use the quadratic formula in maths and when do i have to work it out not using the quadratic formula?
When you have a quadratic of the form ax^2 + bx + c, and ac allows you to split the middle term, then you use factorisation. If not, then you use the quadratic formula. That's it.
this sounds really dumb but if it is a solve question can i use it then?
Original post by amelia.c.r
when can i use the quadratic formula in maths and when do i have to work it out not using the quadratic formula?
It's not always obvious. Some rules to follow:
If a question says something which indicates that the solutions are not integers or fractions then it won't be possible to factorise the quadratic. So use the quadratic formula (or complete the square). E.g. "give your answers to 2 d.p" or "give your answers in this surd form". And vice-versa, if you know the solutions are integers or fractions then it must be possible to factorise the quadratic
And obviously if a question tells you to factorise or use the formula then you do what the question says.
If you are just given a quadratic with no indication of which method to use then it's worth spending a bit of time trying to factorise the quadratic, especially if the quadratic has low coefficients because using the formula generally takes longer. If you are spending too long then just use the quadratic formula instead.
Make sure you practice lots of exam questions. With practice you will be able to judge better which quadratics feel like they factorise or not.
Original post by toxicgamage56
When you have a quadratic of the form ax^2 + bx + c, and ac allows you to split the middle term, then you use factorisation. If not, then you use the quadratic formula. That's it.
Worth pointing out that many students don't use this method to factorise quadratics and won't know what you mean here.
Original post by Notnek
Worth pointing out that many students don't use this method to factorise quadratics and won't know what you mean here.
Do you mean something like this?
If it was:
8x^2+5x+3
Then you would make it:
8x^2+2x+3x+3
Then factorise:
2x(4x+1)+3(x+1)
If it was a proper question then I would make it into two brackets.
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