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7) 78 x 78 = 80.80 – 4.80 + 4 = 6400 – 316 = 6084

8) 88 x 88 = 90.90 – 4.90 + 4 = 8100 – 356 = 7744

9) 98 x 98 = 100.100 – 4.100 + 4 = 10000 – 396 = 9604

8.2.7 Perkalian dua digit dengan satuan 7

1) 17 x 17 = 20.20 – 3.2.20 + 3.3 = 400 – 120 + 9 = 289

atau

17 x 17 = 20.20 – 6.20 + 9 = 400 – 120 + 9 = 289

2) 27 x 27 = 30.30 – 6.30 + 9 = 900 – 180 + 9 = 729
3) 37 x 37 = 40.40 – 6.40 + 9 = 1600 – 240 + 9 = 1369

4) 47 x 47 = 50.50 – 6.50 + 9 = 2500 – 300 + 9 = 2209
5) 57 x 57 = 60.60 – 6.60 + 9 = 3600 – 360 + 9 = 3249

6) 67 x 67 = 70.70 – 6.70 + 9 = 4900 – 420 + 9 = 4489

7) 77 x 77 = 80.80 – 6.80 + 9 = 6400 – 480 + 9 = 5929

8) 87 x 87 = 90.90 – 6.90 + 9 = 8100 – 540 + 9 = 7569

9) 97 x 97 = 100.100 – 6.100 + 9 = 10000 – 600 + 9 = 9409

8.2.8 Perkalian dua digit dengan satuan 6

1) 16 x 16 = 20.20 – 4.2.20 + 4.4 = 400 – 160 + 16 = 256
atau

16 x 16 = 20.20 – 8.20 + 16 = 400 – 160 + 16 = 256

2) 26 x 26 = 30.30 – 8.30 + 16 = 900 – 240 + 16 = 676

3) 36 x 36 = 40.40 – 8.40 + 16 = 1600 – 320 + 16 = 1296

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