Bila P dan Q akar-akar persamaan kuadrat x^2 + 5x + 3 = 0, maka nilai dari P^2 - Q^2 = A. 10 B. 11 C. 12 D. 13 E. 14

x^2 + 5x + 3 = 0
Ditanya : P^2 - Q^2 = ...?
Jawab :
P^2 - Q^2
= (P + Q)^2 - 4.P.Q
= (-b/a)^2 - 4(c/a)
= (-5/1)^2 - 4(3/1)
= 25 - 12
= 13

x^2 + 5x + 3 = 0
D = b^2 - 4ac = 5^2 - 4(1)(3) = 25 - 12 = 13
p + q = -b/a = -5/1 = -5
p - q = ± √D / a = ± √13 / 1 = ± √13

p^2 - q^2 = (p + q)(p - q)
Jika p > q => -5 . √13 = -5√13
Jika p < q => -5 . -√13 = 5√13