S=100+1200

Постоянная часть ежемесячного платежа
(выплата основного долга):
1й-15й месяцы: (1300-100):15=80 тыс руб
16й месяц: 100 тыс руб

Переменная часть ежемесячного платежа
(выплата процентов):
1й месяц: (100+1200)*r=(100+15*80)r
2й месяц:  =(100+14*80)r
3й месяц:  =(100+13*80)r
...
14й месяц:  =(100+2*80)r
15й месяц:  =(100+1*80)r
16й месяц:  =(100)r

Сумма всех постоянных платежей:
80*15+100=1300 - тело кредита

Сумма всех переменных платежей
(сумма всех процентов):
16*100r+80r*(15+14+...+2+1)=
=1600r+80r*(15+1)*15/2=
=1600r+80r*15*8=1600r+9600r=
=11200r

Полная сумма выплат =1300+11200r =1636
r=(1636-1300)/11200=0.03=3%

A = Point(yAxis)
B = (15, 1)
f = Segment(A, B)
C = Point(xAxis)
g = Segment(B, C)
D = (0.49, 13.402)
E = Point(xAxis)
h = Segment(D, E)
F = Point(f)
G = (1, 0)
i = Segment(F, G)
H = (1.49, 12.602)
I = Point(xAxis)
j = Segment(H, I)
J = Point(f)
K = Point(xAxis)
k = Segment(J, K)
L = (2.45, 11.802)
M = Point(xAxis)
l = Segment(L, M)
N = (3.03, 10.562)
O = (3, 0)
m = Segment(N, O)
P = (3.47, 11.022)
Q = (3.45, 0.062)
n = Segment(P, Q)
R = Point(f)
S = (4, 0)
p = Segment(R, S)
T = (4.41, 10.222)
U = Point(xAxis)
q = Segment(T, U)
V = Point(f)
W = Point(xAxis)
r = Segment(V, W)
Z = (5.45, 9.322)
A_1 = Point(xAxis)
s = Segment(Z, A_1)
B_1 = Point(f)
C_1 = Point(xAxis)
t = Segment(B_1, C_1)
D_1 = (6.43, 8.522)
E_1 = Point(xAxis)
a = Segment(D_1, E_1)
F_1 = Point(f)
G_1 = Point(xAxis)
b = Segment(F_1, G_1)
H_1 = (7.45, 7.762)
I_1 = Point(xAxis)
c = Segment(H_1, I_1)
J_1 = Point(f)
K_1 = Point(xAxis)
d = Segment(J_1, K_1)
L_1 = (8.47, 7.002)
M_1 = Point(xAxis)
e = Segment(L_1, M_1)
N_1 = Point(f)
O_1 = Point(xAxis)
f_1 = Segment(N_1, O_1)
P_1 = (9.49, 6.262)
Q_1 = Point(xAxis)
g_1 = Segment(P_1, Q_1)
R_1 = Point(f)
S_1 = Point(xAxis)
h_1 = Segment(R_1, S_1)
T_1 = (10.47, 5.302)
U_1 = Point(xAxis)
i_1 = Segment(T_1, U_1)
V_1 = Point(f)
W_1 = Point(xAxis)
j_1 = Segment(V_1, W_1)
Z_1 = (11.47, 4.542)
A_2 = Point(xAxis)
k_1 = Segment(Z_1, A_2)
B_2 = Point(f)
C_2 = Point(xAxis)
l_1 = Segment(B_2, C_2)
D_2 = (12.53, 3.722)
E_2 = (12.53, 0.002)
m_1 = Segment(D_2, E_2)
F_2 = Point(f)
G_2 = Point(xAxis)
n_1 = Segment(F_2, G_2)
H_2 = (13.49, 2.962)
I_2 = Point(xAxis)
p_1 = Segment(H_2, I_2)
J_2 = Point(f)
K_2 = Point(xAxis)
q_1 = Segment(J_2, K_2)
L_2 = (14.49, 2.122)
M_2 = Point(xAxis)
r_1 = Segment(L_2, M_2)
N_2 = Point(xAxis)
s_1 = Segment(B, N_2)
O_2 = (15.51, 1.262)
P_2 = (15.47, -0.018)
t_1 = Segment(O_2, P_2)
Q_2 = Intersect(xAxis, yAxis)
a_1 = Segment(A, Q_2)
b_1 = Segment(A, D)
c_1 = Segment(D, F)
d_1 = Segment(F, H)
e_1 = Segment(H, J)
f_2 = Segment(J, L)
g_2 = Segment(L, N)
h_2 = Segment(N, P)
i_2 = Segment(P, R)
j_2 = Segment(R, T)
k_2 = Segment(T, V)
l_2 = Segment(V, Z)
m_2 = Segment(Z, B_1)
n_2 = Segment(B_1, D_1)
p_2 = Segment(D_1, F_1)
q_2 = Segment(F_1, H_1)
r_2 = Segment(H_1, J_1)
s_2 = Segment(J_1, L_1)
t_2 = Segment(L_1, N_1)
a_2 = Segment(N_1, P_1)
b_2 = Segment(P_1, R_1)
c_2 = Segment(R_1, T_1)
d_2 = Segment(T_1, V_1)
e_2 = Segment(V_1, Z_1)
f_3 = Segment(Z_1, B_2)
g_3 = Segment(B_2, D_2)
h_3 = Segment(D_2, F_2)
i_3 = Segment(F_2, H_2)
j_3 = Segment(H_2, J_2)
k_3 = Segment(J_2, L_2)
l_3 = Segment(L_2, B)
m_3 = Segment(B, O_2)
n_3 = Segment(O_2, C)
R_2 = Point(a_1)
p_3 = Segment(F, R_2)
S_2 = Point(a_1)
q_3 = Segment(J, S_2)
T_2 = Point(a_1)
r_3 = Segment(N, T_2)
U_2 = (-0.05, 9.782)
s_3 = Segment(R, U_2)
V_2 = Point(a_1)
t_3 = Segment(V, V_2)
W_2 = Point(a_1)
a_3 = Segment(B_1, W_2)
Z_2 = Point(a_1)
b_3 = Segment(F_1, Z_2)
A_3 = Point(a_1)
c_3 = Segment(J_1, A_3)
B_3 = Point(a_1)
d_3 = Segment(N_1, B_3)
C_3 = (0, 5)
e_3 = Segment(R_1, C_3)
D_3 = Point(a_1)
f_4 = Segment(V_1, D_3)
E_3 = Point(a_1)
g_4 = Segment(B_2, E_3)
F_3 = Point(a_1)
h_4 = Segment(F_2, F_3)
G_3 = (0.03, 1.782)
i_4 = Segment(J_2, G_3)
H_3 = Point(a_1)
j_4 = Segment(B, H_3)
k_4 = Segment(A, D)
l_4 = Segment(A, D)
I_3 = Point(e_1)
m_4 = Segment(F, I_3)
n_4 = Segment(A, D)
p_4 = Segment(D, A)
q_4 = Segment(D, A)
J_3 = Point(c_1)
r_4 = Segment(J_3, A)
K_3 = Point(g_2)
s_4 = Segment(J, K_3)
L_3 = Point(i_2)
t_4 = Segment(N, L_3)
M_3 = Point(k_2)
a_4 = Segment(R, M_3)
N_3 = Point(m_2)
b_4 = Segment(V, N_3)
O_3 = Point(p_2)
c_4 = Segment(B_1, O_3)
P_3 = Point(r_2)
d_4 = Segment(F_1, P_3)
Q_3 = Point(t_2)
e_4 = Segment(J_1, Q_3)
R_3 = Point(b_2)
f_5 = Segment(N_1, R_3)
S_3 = (10.61, 5.022)
g_5 = Segment(R_1, S_3)
T_3 = Point(f_3)
h_5 = Segment(V_1, T_3)
U_3 = Point(h_3)
i_5 = Segment(B_2, U_3)
j_5 = Segment(F_2, H_2)
V_3 = Point(j_3)
k_5 = Segment(F_2, V_3)
W_3 = Point(l_3)
l_5 = Segment(J_2, W_3)
m_5 = Segment(B, O_2)
Z_3 = Point(n_3)
n_5 = Segment(Z_3, B)