Answer:
The function rule is:
![y=-(1)/(2) x-1](https://img.qammunity.org/2021/formulas/mathematics/high-school/kv3yzpew0ys9snqp98f8ayahbwfmp6sx1y.png)
Explanation:
We identify the output with the variable "y", the "input with the variable"x". Notice also that the "opposite of the input is "-x" (negative x), and therefore the words "the output is one less than half of the opposite of the input" translate into:
![y=(1)/(2) (-x)-1\\y=-(1)/(2) x-1](https://img.qammunity.org/2021/formulas/mathematics/high-school/f49lr008pwvg3oyq2a2xn14dxc3dma185i.png)