3^(21)+3^(22)+3^(23)=3^(21)*(1+3+3^2)=3^(21)*13
P = 2(a + b) = 10
S = a*b = 6
a + b = 5
a*b = 6
a = 5 - b
b(5 - b) - 6 = 0 *
* - b^2 + 5b - 6 = 0
b^2 - 5b + 6 = 0
D = 25 - 24 = 1
b1 = ( 5 + 1)/2 = 6 /2 = 3;
b2 = ( 5 - 1)/2 = 4/2 = 2;
a1 = 5 - b1 = 5 - 3 = 2
b1 = 3
a2 = 5 - b2 = 5 - 2 = 3
b2 = 2
3х²+5х-8=0
Д=25-4*3*(-8)
Д=121
х1=(-5+11)/6
х2=(-5-11)/6
х1=1
х2==-8/3=-2 2/3
1*(-2 2/3)=-2 2/3
1/5 = 0,2
0,2х + 0,62х + 12,96 = х
0,64х - х = - 12,96
-0,36х = - 12,96
Х = 36