Write the systematic IUPAC names of the following compounds :
`C_6 H_5 - CH=CH-COOH`

Explanation

To write the systematic IUPAC name for the compound \( C_6H_5 - CH=CH - COOH \), we will follow these steps:

### Step 1: Identify the longest carbon chain
The compound consists of a phenyl group (C6H5) attached to a carbon chain that includes a double bond and a carboxylic acid group (COOH). The longest carbon chain that includes the functional groups is three carbons long.

### Step 2: Number the carbon chain
We will number the carbon chain starting from the end closest to the carboxylic acid group (COOH). This gives us:
- Carbon 1: COOH (carboxylic acid)
...