Concept:
Binary operations are rules that combine two elements to produce a third. To solve nested operations, follow the order of operations by resolving the expression inside the parentheses first, then using that result for the outer operation.
Step 1: Evaluate the expression inside the parentheses.
Using the definition $a \oplus b = a^2 + b^2$:
\[ 2 \oplus 3 = 2^2 + 3^2 = 4 + 9 = 13 \]
Step 2: Perform the outer operation.
Substitute the result from Step 1 back into the full expression:
\[ (2 \oplus 3) \oplus 4 = 13 \oplus 4 \]
Apply the definition again:
\[ 13 \oplus 4 = 13^2 + 4^2 = 169 + 16 = 185 \]