Calculation: midA7t - 1

V_2  = 
 V_1* (1+ 3* α* Δ_t)
V_2 =  V_1* (1+ 3* α* Δ_t)$$V_{2}$$ = $$V_{1}\cdot (1+3\cdot \alpha\cdot \Delta_{t})$$
V_2 = V_1+ 3* Δ_t* α* V_1$$V_{2}$$ = $$V_{1}+3\cdot \Delta_{t}\cdot \alpha\cdot V_{1}$$
V_2 = V_1+ 3* V_1* Δ_t* α$$V_{2}$$ = $$V_{1}+3\cdot V_{1}\cdot \Delta_{t}\cdot \alpha$$