Factor.
-16 + 17(5-y²)-(5-y²)²
and
[x + y + 1][x² - x(y + 1)+(y + 1)²
#1
-16 + 17(5-y²)-(5-y²)²
let X = (5-y²)
-16 + 17X - X²
-(16 - 17X + X²)
-(X² - 17X + 16)
-(X - 16)(X - 1)
substituting back X,
-((5-y²) - 16)((5-y²) - 1) or
(11 - y²)(4 - y²)
#2
[x + y + 1][x² - x(y + 1)+(y + 1)²]
let A = y + 1
[x + A][x² - xA + A²]
notice that this is sum of two cubes. therefore,
x^3 + A^3
substituting back A,
x^3 + (y+1)^3
hope this helps~ :)