ОбъяснФормулы n-го члена и суммы n членов известны
an = a1 + d*(n - 1)
S(n) = (a1 + an)*n/2 = (2a1 + d*(n-1))*n/2
1) a1 = -5, n = 23, S(n) = 1909
1909 = (-2*5 + d*22)*23/2 = (-5 + 11d)*23
-5 + 11d = 1909/23 = 83
11d = 88, d= 8
2) a1 = -3,87, d= -2,77 + 3,87 = 1,1, n = 10
a10 = a1 + 9d = -3,87 + 9*1,1 = 9,9 - 3,87 = 6,03
S(10) = (-3,87 + 6,03)*10/2 = 2,16*5 = 10,8
3) a2 = a1 + d= 2, a9 = a1 + 8d = 6,9
a9 - a2 = 7d = 6,9 - 2 = 4,9
d= 0,7
4) 1) x1 = 3 + 2 = 5, x2 = 6 + 2 = 8, d= 3
S(20) = (2*5 + 3*19)*20/2 = (10 + 57)*10 = 670
2) x1 = 4 - 9 = -5, x2 = 8 - 9 = -1, d= 4
S(30) = (-2*5 + 4*29)*30/2 = (-10 + 116)*15 = 1590
5) 1) d= 2, an = 49, S(n) = 702
Система
{ an = a1 + d(n-1) = a1 + 2(n-1) = 49
{ S(n) = (a1 + an)*n/2 = (a1 + 49)*n/2 = 702
{ a1 + 2n = 49 + 2 = 51
{ a1*n + 49n = 702*2 = 1404
{ a1 = 51 - 2n
{ (51 - 2n)*n + 49n - 1404 = 0
-2n^2 + 100n - 1404 = 0
n^2 - 50n + 702 = 0
(n - 27)(n - 13) = 0
n = 13, a1 = 51 - 26 = 25
n = 27, a1 = 51 - 54 = -3
2) an = 18 - 2n, S(n) = n*(17 - n)
an = a1 + d(n-1) = a1-d + dn = 18 - 2n
S(n) = (2a1 + d(n-1))*n/2 = n*(17 - n)
Система
{ (a1-d) + dn = 18 - 2n
{ (2a1-d) + dn = 2(17 - n) = 34 - 2n
Из 2 уравнения вычитаем 1 уравнение
a1 = 34 - 18 = 16
Подставляем обратно в 1 уравнение
16 + dn - d = 18 - 2n
dn - d = 2 - 2n
d(n - 1) = -2(n - 1)
d= -2ение:
1) y=2sin(4x)-8cos(x/4)+(1/2)*tg(2x)-(1/12)*ctg(6x)
y ' =8cos(4x)+2sin(x/4)+1/cos^2(x)+sin^2(x)/2
2) y=sin(x/4)+12cos(x/3)-10tg(x/2)+5ctg(2x)
y ' = cos(x/4)/4-sin(x/3)/3-5/cos^2(x/2)+2*sin^2(2x)/5
3) y=(8/12)*sin(3x/4)-(4/3)*cos(3x/4)-40ctg(x/5)-tg(8x)
y ' = (1/2)*sin(3x/4)+sin(3x/4)+8/sin^2(x)-8/cos^2(x)
4) y =cos(2x)*x^5
y ' =-2sin(2x)*x^5+5cos(2x)*x^4
5) y=sin(2x)/cos(4x)
y ' =2cos(2x)/cos(4x)+4sin(2x)/cos^2(4x)
6) y=8cos(4x-pi/3)
y ' =-32sin(4x-pi/3)
7) y=10x^5+7x^4-8x^3+4/x-9sqrt(x)-4x+1,1
y ' = 50x^4+28x^3-24x^2-4/x^2-9/2*sqrt(x)-4
8) y=sin(3x)*tg(3x)
y ' = 3cos(3x)*tg(3x)+sin(3x)*3/cos^2(3x)
9) y=5x^6+2x^3+6x^2-6x-8
y ' = 30x^5+6x^2+12x-6
y '' = 150x^4+12x+12
10) y=4sin(2x)-16cos(4/x)
y ' = 8cos(2x)+64sin(x/4)/x^2
y '' =-16sin(2x) +16cos(x/4)/x^2-128sin(x/4)/x^3
