Analyze the mathematical expressions on the blackboard.

Mathematical Expressions:

• 16x⁶y¹² - 64a², 49x² - 144b²
• N 998(i, gil, y)
• N 891(δ)

Analysis: The image contains mathematical expressions and notations. The first line appears to be a subtraction of two terms involving variables x, y, and a, as well as x and b, with exponents. The subsequent lines contain notations that seem to represent specific problems or variables, possibly from a textbook or assignment, indicated by 'N' followed by numbers and parenthetical elements like '(i, gil, y)' and '(δ)'. These could refer to problem numbers or specific parameters within a mathematical context.