How to know if equation can be solved by factorising before trying? So, I have core 1 test tomorrow and there is a lot of solving of quadratic equations without calculator and my weakest point is the time I waste in trying to factorise and equation but then it ends up it doesn't factorise or the opposite way in which I use equation while I could've done factorising. Is there any way you can know if equation factorise or not?
Check the discriminant. If it is a perfect square, the radical expression in the quadratic formula becomes an integer (I'm assuming you've cleared fractions before beginning the problem, and all coefficients are integers after that).

Recall that the discriminant for $ax^2 + bx + c = 0$ is $\Delta = b^2-4ac$, and that the solution(s) are $$x = \frac{-b\pm\sqrt{\Delta}}{2a}$$

I'm also assuming you're only interested in factoring if you can do it without using radicals. For example, you could factor $x^2-2$ as $(x+\sqrt{2})(x-\sqrt{2})$, but I'm guessing that doesn't interest you.
For example,
x2+6x+10
x2+6x+10
could only have m,nm,n as (1,10)(1,10) or (2,5)(2,5); since neither of those add up to 66 you can't factor this with easy factors.

The other way is to find b2−4acb2−4ac. If that is a perfect square, then the equation can be factored nicely. If not, then at least you are halfway toward finding the roots using the quadratic formula.