21.(本小题10分)利用因式分解简便计算：
(1)$3^2 × 2026 + 42 × 2026 + 7^2 × 2026$.
(2)$65^2 × 10 - 35^2 × 10$.

21.【解】(1)原式$= 2026 × (3^2 + 42 + 7^2) = 2026 × (3 + 7)^2 = 2026 × 100 = 202600$.(2)原式$= 10 × (65^2 - 35^2) = 10 × (65 + 35) × (65 - 35) = 10 × 100 × 30 = 30000$.