syms ZL ZR1 ZR2 real

%

Ze = 1 / (1 / ZL + 1 / ZR2)

%

Z = Ze / (Ze + ZR1)

%

syms R1 R2 L w real

%

Z = subs(Z, ZR1, R1)
Z = subs(Z, ZR2, R2)
Z = subs(Z, ZL, i * w * L)

%

a = simplify(real(Z))

%

b = simplify(imag(Z))

%

a/b