1) (a²-5)(a²+5)=а^4+5а²-5а²-25=а^4-25
2) (4-x²) (4+x²) =16+4х²-4х²-x^4=16-x^4
3) (9x-y²) (9x+y²)=81х²+9ху²-9ху²-у^4=81х²-у^4
1) (a²-5)(a²+5)=а^4+5а²-5а²-25=а^4-25
2) (4-x²) (4+x²) =16+4х²-4х²-x^4=16-x^4
3) (9x-y²) (9x+y²)=81х²+9ху²-9ху²-у^4=81х²-у^4