(5а^2-3b)(5а^2+3b)=25b^4 - 9b^2
(4m^2+6n)(4m^2-6n)=16m^4 - 36n^2
1) (5а^2-3b)(5а^2+3b)=25a^4+15a^2b-15a^2b-9b^2=25a^4-9b^2
2) (4m^2+6n)(4m^2-6n)=16m^4-24m^2n+24m^2n-36n^2=16m^4-36n^2
