1. (30 pts) For each of the following systems, determine whether it is linear and whether it is time-invariant. Justify your answers. If it is LTI, find the impulse response

function h(t). Each system is specified by the output y that is produced from an input r. \text { (a) } y(t)=x(t+7) \text { (b) } y(t)=x(3 t) \text { (c) } y(t)=|x(10)| y(t)=\int_{-\infty}^{\infty} I_{[0,+\infty)}(t-\tau) \exp (\tau-t) x(\tau) d \tau y(t)=\int_{-\infty}^{\infty} \frac{1}{1+\tau^{2}} x(\tau-t) d \tau y(t)=\int_{-1}^{0}(\tau-1) x(t+\tau) d \tau y(t)=\min (1, \max (-1, x(t-4))) n) Let (a1,. , ak) be a vector of k nonnegative reals and let (T1,.., Tk) E R*. y(t)=\underset{x \in \mathbb{R}}{\operatorname{argmin}} \sum_{i=1}^{k} a_{j}\left(z-x\left(t-\tau_{i}\right)\right)^{2} The argmin, is the value of z (the argument) that minimizes the expression.