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Verified answer
Kelas 10 MatematikaBab Persamaan Kuadrat
x + 3 = a
x = a - 3
x² - 3x - 21 = 0
(a - 3)² - 3 (a - 3) - 21 = 0
a² - 6a + 9 - 3a + 9 - 21 = 0
a² - 9a - 3 = 0
x² - 9x - 3 = 0