intr = bal.n * r bal.n+1 = bal.n + intr - pmt bal.1 = bal.0 + intr.0 - pmt bal.2 = bal.1 + intr.1 - pmt bal.3 = bal.2 + intr.2 - pmt bal.3 = (bal.1 + intr.1 - pmt) + intr.0 - pmt bal.3 = bal.0 + intr.0 + intr.1 + intr.2 + intr.3 - 4pmt bal.n = bal.0 + intr.0 + [... + intr.n ] - (n+1)pmt bal.3 = (bal.1 + intr.1 - pmt) + intr.0 - pmt bal.3 = bal.0 + intr.0 + intr.1 + intr.2 + intr.3 - 4pmt bal.n = bal.0 + intr.0 + [... + intr.n ] - (n+1)pmt intr.0 + intr.1 + intr.2 = (bal.0 * r) + (bal.1 * r) + (bal.2 *) r* (bal.0 + bal.1 + bal.2) r* (bal.0 + bal.1 + bal.2)