Question

Factorise: 15(2x - y)² - 16(2x - y) - 15  

Answer 1

15(2x - y)² - 16(2x - y) - 15  

= Let 2x - y = a, then

15a² - 16a - 15

= 15a² - 25a + 9a - 15   
    ...{15 × (-15) = -225 , -225 = -25 × 9 , -16 = -25 + 9}

= 5a (3a - 5) + 3(3a - 5)

= (3a - 5)(5a + 3)

= [3 (2x - y) - 5][5 (2x - y) + 3]

= (6x - 3y - 5)(10x - 5y + 3)