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(4-n)(5-n)=12 . Află n.

Răspuns :

20-4n-5n+n^2=12   (n^2 inseamna n la puterea a 2)
20-9n+n^2=12
20-12-9n+n^2=0
18-9n+n^2=0
a=18 b=9 c=1
aflam Discriminantul (delta)
∆=b^2-4ac=9^2-4*18*1=9
aflam solutiile x1 si x2
x1=-b-√∆/2a=0.(3)
x2=-b+√∆/2a=0.1(6) 
raspuns: 0.(3) si 0.1(6)