Let x=x(t) and y=y(t) be solutions of the differential equations dxdt+ax=0 and dydt+by=0 respectively, a, b . Given that x(0)=2; y(0)=1 and 3y(1)=2x(1), the value of t, for which x(t)=y(t), is :
- 232
- 432
- 4 3
- 3 4
Answer
(2) 432
Solution
Separate variables: dxx=-a dt
x=x(0)e-at=2e-at
Similarly y=y(0)e-bt=e-bt
3y(1)=2x(1) 3e-b=4e-a ea-b= 43
x(t)=y(t) 2e-at=e-bt e(a-b)t=2
( 43 )t=2 t= 432
Answer: (2)