=] 又係maths 紅色圈圈

1b.
Put y = -3, x = -2 into y = ax^2 + x + 3
-3 = (-2)^2．a + (-2) + 3
-3 = 4a – 2 + 3
4a = -4
a = -1

2a.
f(1) + f(-1)
= 1 ÷ (1^2 + 3) + (-1) ÷ [(-1)^2 + 3]
= 1 ÷ 4 + (-1) ÷ 4
= 0.25 – 0.25　　OR　　1/4 – 1/4
= 0

2b.
f(2)．f(-2)
= [2 ÷ (2^2 + 3)]．{(-2) ÷ [(-2)^2 + 3]}
= (2 ÷ 7)．[(-2) ÷ 7]
= 2/7．(-2/7)
= -4/49


^2 = square
因為顯示唔到二次,所以用^2代替square.