Jawab:

Penjelasan dengan langkah-langkah:

1. Bentuk umum persamaan kuadrat adalah ax² + bx + c = 0.

21 - 20x - x² = 0

-x² - 20x + 21 = 0

Sehingga nilai a = -1, b = -20 dan c = 21.

2. (x + 4)(2x - 5) = 0

(x + 4)(2x) - (x + 4)(5) = 0

2x² + 8x - 5x - 20= 0

2x² + 3x - 20 = 0

3. a. 2x² - 10x = 0

2x (x - 5) = 0

2x = 0

x = 0

x - 5 = 0

x = 5

HP = {0, 5}

b. 16h² - 9 = 0

(4h - 3) (4h + 3) = 0

4h - 3 = 0

4h = 3

h = ¾

4h + 3 = 0

4h = -3

h = -¾

HP = {-¾, ¾}

c. x² + 7x - 8 = 0

(x - 1) (x + 8) = 0

x - 1 = 0

x = 1

x + 8 = 0

x = -8

HP = {-8, 1}

d. 2x² + 6x + 4 = 0​

x² + 3x + 2 = 0​

(x + 1) (x + 2) = 0

x + 1 = 0

x = -1

x + 2 = 0

x = -2

HP = {-2, -1}