Solve 9^a - 10 * 3^a + 9 = 0

Sure.

or, 9^a - 10 × 3^a + 9 = 0
or, 3^2a - 10 × 3^a + 9 = 0

let 3^a = k

or, k² - 10.k + 9 = 0
or, k² - (9 + 1)k + 9 = 0
or, k² - 9k - k + 9 = 0
or, k(k - 9) - 1(k - 9) = 0
or, (k - 9)(k - 1) = 0

Either, k = 9
so, 3^a = 3²
so, a = 2

OR, k = 1
so, 3^a = 3⁰
so, a = 0

∴ a = 0, 2

Video explanation: