Answer :

MichaelLiu
[tex] n^{2} -7n+12[/tex]
The best way to improve your skill factoring this trinomials is just to practice and practice again. 
So basically we need 2 numbers that multiply to 12 and that add up to -7. Using some intuition and some guess and check, we learn that the 2 numbers are -4 and -3. Putting them into 2 binomials, we get 
[tex](n-4)(n-3)[/tex]
(n-4)(n-3)

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Sancak19o7
[tex]n^2-7n+12=0 \\ \\ (n-4)(n-3)=0 [/tex]
if it equal 0 
[tex]n^2-7n+12=0 \\ \\ (n-4)(n-3)=0 \\ n-4=0 \\ n=4 \\ \\ n-3=0 \\ n=3 \\ \\ x_1=4,x_2=3 [/tex]