Consider a linear time-invariant system whose input $\text{r(t)}$ and output $\text{y(t)}$ are

related by the following differential equation:

$$\frac{d^{2}y\left ( t \right )}{dt^{2}}+4y\left ( t \right )=6r\left ( t \right )$$

The poles of this system are at

1. $+2j,-2j$
2. $+2,-2$
3. $+4,-4$
4. $+4j,-4j$
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