Factorise: `y^(2)-121`

Answer

To factorise the expression \( y^2 - 121 \), we can follow these steps:

### Step 1: Recognize the difference of squares
The expression \( y^2 - 121 \) can be recognized as a difference of squares. The general form of a difference of squares is \( a^2 - b^2 \), which can be factored into \( (a + b)(a - b) \).

### Step 2: Identify \( a \) and \( b \)
In our case:
- \( a^2 = y^2 \) implies \( a = y \)
- \( b^2 = 121 \) implies \( b = 11 \) (since \( 11^2 = 121 \))

### Step 3: Apply the difference of squares formula
Now we can apply the difference of squares formula:
\[ y^2 - 121 = (y + 11)(y - 11) \]

### Step 4: Write the final answer
Thus, the factorised form of \( y^2 - 121 \) is:
\[ (y + 11)(y - 11) \]

### Final Answer:
\[ y^2 - 121 = (y + 11)(y - 11) \]

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