F4 maths 一元二次方程(2)

1) a) x² – 4x + 3 = 0(x –3)(x – 1) = 0 x = 3 or x = 1 b) y =6 or y = 2 y² – (6 + 2)y + (6*2) = 0y² – 8y + 12 = 0

2012-12-12 18:39:29 補充：
Little reminder:
ax² + bx + c = 0, x = α or x = β;
α + β = - b/a, αβ = c/a;
x² - (α + β)x + αβ = 0

(a)a^2-4a+3=0

a -3
a -1

-3a-1a=-4a

a-3=0
a-1=0

so a=3 or a=1


(b)x=6,x=2

x -6
x -2
-6x-2x=-8x

so x^2-8x+(-6)(-2)=0
x^2-8x+12=0

so y=x^2-8x+12