15. Вычислить значение выражения:

1) (x²y^-2 - 4y^-2) * (1/y)^-2 = (5² * 6,7^-2 - 4 * 6,7^-2) * 6,7² = (25 * 6,7^-2 - 4 * 6,7^-2) * 6,7² = (21 * 6,7^-2) * 6,7² = 21
2) ((a²b^-1)⁴ - a⁰b⁴) / (a⁴ - b⁴) / b² = ((2² * (-3)^-1)⁴ - 1 * (-3)⁴) / (2⁴ - (-3)⁴) / (-3)² = ((4 * (-1/3))⁴ - 81) / (16 - 81) / 9 = ((-4/3)⁴ - 81) / (-65) / 9 = (256/81 - 81) / (-65) / 9 = ((256 - 6561)/81) / (-65) / 9 = (-6305/81) / (-65) / 9 = (6305/81) * (1/65) * (1/9) = 97/729