Math & Chem

Ho Yiu

2009-10-04 12:04 am

Math
1. Let k be a constant. If the quadratic equation x^2 + 14x + k = 0 has no real roots, find the range of values of k.

2. The quadratic equation 9x^2 - (k+1) x + 1 = 0 . . . ( * )
has equal roots.
(a) Find the two possible values of the constant k.
(b) If k takes the negative value obtained, solve equation ( * ).

Chem
1. To grind a soild into a fine powder, use _____ and ____.
2. To dry solids and liquids, place them in a _____.
3. Which of the following chemicals are toxic?
(1)Ammonia
(2)Carbon monoxide
(3)Sodium

回答 (1)

Prof. Physics

2009-10-04 8:54 pm

✔ 最佳答案

1. x2 + 14x + k = 0 has no real roots,

Discriminant < 0

(14)2 - 4(1)k < 0

4k > 196

k > 49

2.a. 9x2 - (k + 1)x + 1 = 0

With equal roots, discriminant = 0

[-(k + 1)]2 - 4(9)(1) = 0

k2 + 2k - 35 = 0

(k - 5)(k + 7) = 0

k = -7 or 5

For k = -7, the equation is:

9x2 + 6x + 1 = 0

(3x + 1)2 = 0

x = -1/3 (repeated)

1. We use a pestle and a mortar to grind a solid into a fine powder.

2. To dry solids and liquids, place them in a desiccator.

3. Ammonia and carbon monoxide are toxic.

參考: Physics king

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