Penjelasan dengan langkah-langkah:

y = x² - 4x - 21

y = x² - 7x + 3x - 21

y = x(x - 7) + 3 (x - 7)

y = (x + 3)(x - 7)

x + 3 = 0 v x - 7 = 0

x = -3 v x = 7

misal x adalah -5 sampai 9

x = -5 —> y = (-5)² - 4(-5) -21 = 25 + 20 - 21 = 24

x = -4 —> y = (-4)² - 4(-4) -21 = 16 + 16 - 21 = 11

x = -3 —> y = (-3)² - 4(-3) -21 = 9 + 12 - 21 = 0

x = -2 —> y = (-2)² - 4(-2) -21 = 4 + 8 - 21 = -9

x = -1 —> y = (-1)² - 4(-1) -21 = 1 + 4 - 21 = -16

x = 0 —> y = (0)² - 4(0) -21 = 0 + 0 - 21 = -21

x = 1 —> y = (1)² - 4(1) -21 = 1 - 4 - 21 = -24

x = 2 —> y = (2)² - 4(2) -21 = 4 - 8 - 21 = -25

x = 3 —> y = (3)² - 4(3) -21 = 9 - 12 - 21 = -24

x = 4 —> y = (4)² - 4(4) -21 = 16 - 16 - 21 = -21

x = 5 —> y = (5)² - 4(5) -21 = 25 - 20 - 21 = -16

x = 6 —> y = (6)² - 4(6) -21 = 36 - 24 - 21 = -9

x = 7 —> y = (7)² - 4(7) -21 = 49 - 28 - 21 = 0

x = 8 —> y = (8)² - 4(8) -21 = 64 - 32 - 21 = 11

x = 9 —> y = (9)² - 4(9) -21 = 81 - 36 - 21 = 24

sumber gambar : mathway.com/id/Graph