Question

y
$y ^{3} - 7y + 6$
factorise

Answer 1

y^3 - 7y + 6

= y^3 - y - 6y + 6

= y( y^2 - 1) - 6(y-1)

= y [ (y)^2 - (1)^2] - 6(y-1)

= y (y-1)(y+1) - 6(y-1)

= (y-1)(y^2 + y - 6)

= (y - 1) [ y^2 + 3y - 2y - 6]

= (y-1) [ y( y + 3) - 2(y+3)]

= (y-1)(y + 3)(y - 2)