1) a^4 + 4
= a^4 + 4 + 4a² - 4a²
= (a² + 2)² - 4a²
= (a² + 2 - 2a).(a² + 2 + 2a)
2) a^4b^4 +324
= a^4b^4 + 324 + 36a²b² - 36a²b²
= (a²b² + 18)² - 36a²b²
= (a²b² + 18 - 6ab).(a²b² +18 +6ab)
3) a^4b^8 + 64c^4
= a^4b^8 + 64c^4 + 16a²b^4c² - 16a²b^4c²
= (a²b^4 + 8c²)² - 16a²b^4c²
= (a²b^4 + 8c² - 4ab²c).( a²b^4 + 8c² + 4ab²c)