Answer:
≈ 1.1405 Ω/s
Explanation:
Relation: 1/R = 1/R₁ +1/R₂
Derivative: (1/R)²·dR/dt = (1/R₁)²·dR₁/dt +(1/R₂)²·dR₂/dt
With values substituted: (11/280)²·dR/dt = (1/40)²·(2) +(1/70)²·(2.5)
... dR/dt = 2·(7/11)² +2.5(4/11)² = 138/121 . . . . Ω/s
Final answer:
... dR/dt = 138/121 Ω/s ≈ 1.1405 Ω/s