a:=[a3,a4,a5,a6,a7,a8,a9,a10]

[v1(t):=a1*COS(2*pi*f*t)+a2*SIN(2*pi*f*t),v2(t):=a3*COS(2*pi*f*t)+a4*SIN(2*pi~
*f*t),v3(t):=a5*COS(2*pi*f*t)+a6*SIN(2*pi*f*t),v4(t):=a7*COS(2*pi*f*t)+a8*SIN~
(2*pi*f*t),i(t):=a9*COS(2*pi*f*t)+a10*SIN(2*pi*f*t)]

eq:=[0=-i(t)+(v1(t)-v2(t))/r1,0=-i(t)+c*(v2'(t)-v3'(t)),0=-l*i'(t)+v3(t)-v4(t~
),0=-i(t)+v4(t)/r2]

m:=VECTOR(eq,t,[0,1/(4*f)])

s:=(SOLUTIONS(m,a)) SUB 1

;Sub(User')
SUBST(eq,a,s)

v5(a1,a2,t,f):=SUBST(v4(t),a,s)

pulse(t):=5*(SQUARE_WAVE(t)+1)*SIN(2*pi*4*t)*(t-(t-1/5)*STEP(t-1/5)-(t-4/5)*S~
TEP(t-4/5))

FOURIER1(y,t,t1,t2,n):=1/(t2-t1)*INT(y,t,t1,t2)+2/(t2-t1)*SUM(COS(2*pi*m_*t/(~
t2-t1))*INT(y*COS(2*pi*m_*t/(t2-t1)),t,t1,t2)+SIN(2*pi*m_*t/(t2-t1))*INT(y*SI~
N(2*pi*m_*t/(t2-t1)),t,t1,t2),m_,1,n)

FOURIER2(y,t1,t2):=1/(t2-t1)*INT(y,t,t1,t2)

FOURIER3(y,t1,t2,n):=2/(t2-t1)*VECTOR([INT(y*COS(2*pi*m_*t/(t2-t1)),t,t1,t2),~
INT(y*SIN(2*pi*m_*t/(t2-t1)),t,t1,t2)],m_,1,n)

FOURIER4(t1,t2,n):=VECTOR([COS(2*pi*m_*t/(t2-t1)),SIN(2*pi*m_*t/(t2-t1))],m_,~
1,n)

f2:=FOURIER2(pulse(t),0,2)

f3:=FOURIER3(pulse(t),0,2,64)

f4:=FOURIER4(0,2,64)

f5(t):=f2+APPEND(f3)*APPEND(f4)

FOURIER(pulse(t),t,0,2,64)-f5(t)

v6(a1,a2,t,f):=SUBST(v5(a1,a2,t,f),[r1,r2,c,l],[1,1,5/(2*pi*8)^2,1/5])

SUM(v6(f3 SUB m_ SUB 1,f3 SUB m_ SUB 2,t,m_/2),m_,1,64)

5*EXP(-5*t)

EXP(-t)=0.01

;Solve(#21,t)
SOLVE(EXP(-t)=0.01,t)

t=2*LN(10)

;Approx(#23)
t=4.605170185988091368035982909368728415202202977257545952066655801

pulse(t)