The resistance of two conducters in series is 40 ohm and their resistance becomes 7.5 ohm when connected in parallel.Find the resistance of the two individual conductors....{PLEASE SOLVE THIS QUESTION BY THE METHOD OF QUADRATIC EQUATION}

say two resistances are r1 &r2.

r1+r2=40 from the series formula

(r1 xr2)/(r1+r2)=7.5  from the formula of parallel res

so from equ 1 and 2:

r1 xr2=7.5x40=300

r1=300/r2

put this in equ 1:

300/r2  + r2 =40

r2²-40x r2+300=0

(r2-30) (r2-10)=0

r2=30 or 10

simlarly r1=10 or 30