15n-(3n-5)(4n+5)=5-12

Question

15n-(3n-5)(4n+5)=5-12

Answer 1

15n - (12n2 + 15n - 20n - 25) = 5 - 12
15n - 12n2 - 15n + 20n + 25 - 5 + 12 = 0
-12n2 + 20n + 32 = 0 делим на (-2)
6n2 - 10n - 16 = 0 делим на (2)
3n2 - 5n - 8 = 0
D = b2 - 4ac
D = 25 +4*3*8 = 121, корень дискриминанта равен 11
n1 = 5+11:6 = 8/3 = 2 2/3
n2 = 5-11:6 = -1
ответ: 2 2/3 и -1

Answer 2

15n-(3n-5)(4n+5)=5-12
15n-(12n+15n-20n+25)= -7
15n-(7n+25)= -7
15n-7n+25= -7
8n+25= -7
8n= -7-25
8n= -32
n=(-32):8
n= -4