А₁₄=а₁+13d
a₁₄=2,3+13·(-1,9)=-22,4
S₁₄=(a₁+a₁₄):2·14
S₁₄=(2,3-22,4):2·14=-140,7
1)9y^2+6y+1=(3y+1)^2=(3y+1)(3y+1) ;2)um^9+uy^9-ym^9-y^10=u (m^9+y^9)-y (m^9+y^9)=(u-y)(m^9+y^9)
2 ^ ( n + 1 ) - 2^( 3 - n ) = 6
2 ^ n = a ; a > 0
2a - 8•( 1/a ) = 6
( 2a^2 - 8 ) = 6a
2( a^2 - 3a - 4 ) = 0
D = 9 + 16 = 25 = 5^2
a1 = ( 3 + 5 ) : 2 = 4
a2 = ( 3 - 5 ) : 2 = - 1 ( < 0 )
2 ^ n = 4
2 ^ n = 2 ^ 2
n = 2
Ответ 2