helpppp

"Given ab=21-20i  and |b|=29 , find |a|"

Let     \(a=u+iv\text{ , }b=x+iy\)

Then   \(ab=ux-vy+i(vx+uy)\)

so     \(ux-vy=21\\vx+uy=-20\)

Solve these equations to find u and v in terms of x and y.

Then, make use of    \(|b|=\sqrt{x^2+y^2}=29\\\)   to find \(|a|=\sqrt{u^2+v^2}\)

(You should find |a| = 1).

thank you!!!