The total resistance after series connection is two resistors of 10 ohm. When the maximum resistance is possible after parallel connection Give a certain solution process or ideas Maximum total resistance

The total resistance after series connection is two resistors of 10 ohm. When the maximum resistance is possible after parallel connection Give a certain solution process or ideas Maximum total resistance

R1+R2=10
R union = r1r2 / (R1 + R2) = r1r2 / 10
Using the inequality of gentleman in Mathematics:
R1R2 =1/4*(2√R1R2)^2
≤1/4 *(R1+R2)^2 =1/4 * 100 =25
R and ≤ 25 / 10 = 2.5
Maximum resistance: 2.5 Ω