7.
a) (3² * 5ⁿ + 4² * 5ⁿ) : 5ⁿ⁺² = 1
5ⁿ(3² + 4²) : 5ⁿ⁺² = 1
5ⁿ(9 + 16) = 5ⁿ⁺²
5ⁿ * 25 = 5ⁿ * 5²
1 = 1
b) 18 * 7ⁿ - 11 * 7ⁿ = 7ⁿ⁺¹
8 * 7ⁿ - 11 * 7ⁿ = 7ⁿ * 7
7 = 7
8.
a) 5²³ : 5²¹ + 2⁶ * 2⁴ - (2²)⁵ = 5² + 2¹⁰ - 2¹⁰ = 5²
b) 5⁴ * 3⁴ - (15²)² = 5 ⁴ * 3⁴ - 5⁴ * 3⁴ = 5⁴ * 3⁴(1 - 1) = 5⁴ * 3⁴ * 0 = 0
