1) А1=5•1+2=7
А2=5•2+2=12
А3=5•3+2=17
А4=5•4+2=22
2) А25=А1+24d=15+24•3=15+72=87
3) An=A1+d(n–1)=A1+dn–d
A1+dn–d=316
211+15n–15=316
15n=120
n=8
Ответ:А8
4) 1) А6=А1+5d=14+5•(–5)=14–25=–9
(A1+A6)•6
S6 = —————- = (14–9)•3 = 5•3=15
2
2) S50 = (A1+A50)•25 = (12+58)•25=
= 1750
9y = 2x - 1
2y = 3 - 6x
y = 2/9*x - 1/9
y = 3/2 - 3*x
2/9*x - 1/9 = 3/2 - 3x /18
4x - 2 = 27 - 54x
54x + 4x = 27 + 2
58x = 29
x = 29/58
x = 1/2
y = 3/2 - 3*1/2 = 3/2 - 3/2 = 0
Omвem
(1/2; 0 )
<span>5a(a-b+c)+3b(a-b-c)-4c(a+b-c)=5a²-5ab+5ac+3ab-3b²-3bc-4ac-4bc+4c²=
=5a²-3b²+4c²-2ab+ac-7bc</span>