A1+a1+d+a1+2d=21⇒3a1+3d=21⇒a1+d=7⇒d=7-a1
{a1+d-1=a1q⇒a1+7-a1-1=a1q⇒a1q=6
a1+2d+1=a1q²⇒a1+14-2a1+1=a1q²⇒a1q²=15-a1
15-a1=6q
q=(15-a1)/6
a1(15-a1)/6=6
15a1-a1²=36
a1²-15a1+36=0
(a1)1+(a1)2=15 U (a1)1*(a1)2=36
(a1)1=3⇒d1=7-3=4
(a1)2=12⇒d2=7-12=-5
Ответ 3;7;11 или 12;7;2
3х - 5у = - 18
- 2х + 7у = 36
Решение
2х = 7у - 36
Х = 3,5у - 18
3( 3,5у - 18 ) - 5у = - 18
10,5у - 54 - 5у = - 18
5,5у = - 18 + 54
у = 36 : 5,5
у = 36 : ( 11/2 ) = 72/11 = 6 6/11
Х = 7/2 • 72/11 - 18 = ( 252/11 ) - 18 = 22 10/11 - 18 = 4 10/11
Ответ ( 4 10/11 ; 6 6/11 )
1,7*(х-1,2)= 3,2*(х-3,45)
1,7х-2,04=3,2х-11,04
1,7х-3,2х=-11,04+2,04
-15,х= -9
х=6
4X + 7 * ( - 4 ) - 12 = 0
4X - 28 - 12 = 0
4X = 40
X = 10
<span>Ответ. (1+sin(a))/(2*cos(a)+sin(2*a))=(1+sin(a))/(2*cos(a*(1+sin(a))=0,5/(cos(a)) мы в школе делали так </span>