Factorise
` a^(2) + b- ab - a `

Answer

To factorize the expression \( a^2 + b - ab - a \), we will follow these steps:

1. **Rearrange the terms**:
We can rearrange the expression to group similar terms together.
\[ a^2 - ab - a + b \]

2. **Group the terms**:
Now, we can group the first two terms and the last two terms:
\[ (a^2 - ab) + (-a + b) \]

3. **Factor out common terms**:
From the first group \( (a^2 - ab) \), we can factor out \( a \):
\[ a(a - b) + (-1)(a - b) \]
From the second group \( (-a + b) \), we can factor out \(-1\) to make it \( (b - a) \), which is equivalent to \(-(a - b)\).

4. **Factor out the common binomial**:
Now we notice that both terms contain the common factor \( (a - b) \):
\[ (a - b)(a - 1) \]

Thus, the factorized form of the expression \( a^2 + b - ab - a \) is:
\[ (a - b)(a - 1) \]