Khi mắc nối tiếp:

Rtđ=R1+R2=UI=240,6=40(Ω)(1)Rtđ=R1+R2=UI=240,6=40(Ω)(1)

Khi mắc song song:

Rtđ=R1.R2R1+R2=121,6=152⇒R1.R2=152.40=300(Ω)(2)Rtđ=R1.R2R1+R2=121,6=152⇒R1.R2=152.40=300(Ω)(2)

(1),(2)⇒{R1+R2=40(Ω)R1.R2=300(Ω)(1),(2)⇒{R1+R2=40(Ω)R1.R2=300(Ω)

⇔⎧⎪ ⎪ ⎪⎨⎪ ⎪ ⎪⎩R1=300R2300R2+R2=40⇔{R1=300R2300R2+R2=40 ⇔⎧⎪ ⎪ ⎪⎨⎪ ⎪ ⎪⎩R1=300R2300+R22R2=40⇔{R1=300R2300+R22R2=40

⇔⎧⎪⎨⎪⎩R1=300R2(R2−30)(R2−10)=0⇔{R1=300R2(R2−30)(R2−10)=0 ⇔⎡⎢ ⎢ ⎢ ⎢⎣{R1=10(Ω)R2=30(Ω){R1=30(Ω)R2=10(Ω)