Factorise the following expressions.
- \(a^ 2 + 8a + 16 \)
- \(p^ 2 - 10p + 25 \)
- \(25m^2 + 30m + 9 \)
- \(49y^ 2 + 84yz + 36z ^2 \)
- \(4x^ 2 - 8x + 4 \)
- \(121b ^2 - 88bc + 16c ^2 \)
- \((l + m) ^2 - 4lm \) (Hint: Expand \((l + m) ^2 \) first)
- \(a^ 4 + 2a ^2b ^2 + b^ 4\)