Question

Решите срочно ! Нужно на завтра
Туплю

Answer 1

№1
а(1) = -3
а(2) = 4
d = 4-(-3) = 4+3=7
a(n) = a(1) +(n-1)d
a(n) = -3+7(n-1) = -3 + 7n-7 = 7n-10


№2
а(1) = 59
а(2) =55
d = 55-59=-4
a(n) = 59 -4(n-1) = 59 - 4n+4 = 63 - 4n
a(n) > 0
63 - 4n > 0
-4n>-63
n< 63/4
n<15.75 => n = 15
S(15) = (a(1) + a(n))/2 * 15
a(15) = a(1) +14d
a(16) = 59-4*14 = 59-56 = 3
S(16) = (59 + 3) / 2 * 15 = 62 /2 * 15 = 31 * 15 = 465

№3
а) 6х - 5 -(2х+1) = 5х+1 - (6х-5)
6х-5 - 2х-1 = 5х+1 -6х+5
6х-2х-5х+6х = 6+6
5х = 12
х= 2,4

б) 5х+1 - (4х-1) = 4х-1 - (х+5)
5х+1 -4х +1 = 4х-1 -х-5
х+2 = 3х-6
8 = 2х
х=4