Answer:
a²
Step-by-step explanation:
(see attached for reference)
We can find GCF by expressing each expression into their prime factors
7a² = 7 x a x a
8a³b² = 8 x a x a x a x b x b
by observation, we can see that a x a or a² shows up in both expressions, highlighted in bold here:
7a² = 7 x a x a
8a³b² = 8 x a x a x a x b x b
Hence the greatest common factor is a x a = a²
