It's done by special long division: x + x²/a + x³/a² + ∙∙∙ a - x)ax ax - x² x² - x³/a² x³/a² - If you need further explanation, just ask in the note-form below and I'll get back to you by email. Edwin
= = . The very right fraction is the sum of an infinite geometric progression with the first term of "1" and the common ratio of : = 1 + + + + . . . (1) Now multiply both sides of (1) by x, and you will get the required solution = x + + + + . . . QED.