a4+a2b2+b4
Above terms can be written as,
a4+2a2b2+b4−a2b2
(a2)2+2a2b2+(b2)2−(ab)2
(a2+b2)2−(ab)2
(a2+b2+ab)(a2+b−ab)
a+b=8,ab=15
So,(a+b)2=82
a2+2ab+b2=64
a2+2(15)+b2=64
a2+b2+30=64
By transposing,
a2+b2=64−30
a2+b2=34
Then,a4+a2b2+b4
=(a2+b2+ab)(a2+b2−ab)
=(34+15)(34−15)
=49×19
=931