Question 1141584
 Factorise completely: 4b² - ab + (a + 9b)² - a² 
FOIL (a+9b)(a+9b)
4b^2 - ab + a^2 + 18ab +81b^2 - a^2
combine like terms
4b^2 + 81b^2 - ab + 18ab + a^2 - a^2
85b^2 + 17ab
Factor out 17b
17b(5b + a)