I need to compute 987654321² exactly.

Let me use the fact that 987654321 = 10⁹ - 12345679 (since 1000000000 - 987654321 = 12345679).

Using the identity (a - b)² = a² - 2ab + b², where a = 10⁹ and b = 12345679:

987654321² = (10⁹ - 12345679)²
            = (10⁹)² - 2(10⁹)(12345679) + 12345679²

Let me calculate each term:
- (10⁹)² = 10¹⁸ = 1000000000000000000
- 2(10⁹)(12345679) = 2 × 1000000000 × 12345679 = 24691358000000000

Now I need to find 12345679²:
12345679² = 152415765279841

Let me verify this multiplication:
12345679 × 12345679
= 12345679 × (12000000 + 345679)
= 148148748000000 + 4266765279841
= 152415513279841

Let me recalculate more carefully:
12345679 × 12345679
Using standard multiplication:
- 12345679 × 9 = 111111111
- 12345679 × 70 = 864197530
- 12345679 × 600 = 7407407400
- 12345679 × 5000 = 61728395000
- 12345679 × 40000 = 493827160000
- 12345679 × 300000 = 3703703700000
- 12345679 × 2000000 = 24691358000000
- 12345679 × 10000000 = 123456790000000

Adding these up: 152415765279841

Now substituting back:
987654321² = 1000000000000000000 - 24691358000000000 + 152415765279841
            = 1000000000000000000 - 24691358000000000 + 152415765279841
            = 975308642000000000 + 152415765279841
            = 975461057789971041

Therefore, 987654321² = 975461057789971041
