a, `4a² - 12ab + 5b²`
`= (2a)² - 2.2a.3b + (3b)² - 4b²`
`= (2a - 3b)² - (2b)²`
`= (2a - 3b - 2b)(2a - 3b + 2b)`
`= (2a - 5b)(2a - b)`
b, `a^4 + a² + 1 a^4 a^4`
`= a^4 - a + a² + a + 1`
`= a(a - 1)(a² + a + 1) + (a² + a + 1)`
`= (a² + a + 1)(a² - a + 1)`