4х - 5у + 5у + 2х = 18 + 6
6х = 24
х = 4
Если х =4, то 4·4 - 5у =6
5у = 6 + 16
5у = 10
у = 2
Ответ: (4;2)
A12 = a1 + 11d = - 28
a1 - 33 = - 28
a1 = 5
a9 = a1 + 8d = 5 - 24 = - 19
S9 = (5 - 19)*4,5 = - 63
4*(1+cos2x)²/4 -1 =cos2x
(1+cos2x)² -(1+cos2x)=0
(1+cos2x)(1+cos2x-1)=0
(1+cos2x)=0⇒cos2x=-1⇒2x=π+2πn⇒x=π/2+πn⇒x=-π/2∈[-5π/6;π/6]
(1+cos2x-1)=0⇒cos2x=0⇒2x=π/2+πn⇒x=π/4+πn/2⇒x=-3π/4;-π/4∈[-5π/6;π/6]
<span>Подставим число -3 в график 2х²+7х+с=0:
</span><span>2*(-3)²+7*(-3)+с=0
2*9-21+с = 0
18-21+с = 0
с = 3
Уравнение примет вид: </span><span>2х²+7х+3=0
D = 49-4*2*3 = 49 - 24 = 25
</span>
<span>
Ответ: с=3; второй корень -1/2</span>