數學功課難題4!!!!!!!!!急急急急急急急

Question 1: 簡化(cosθ÷1-sin^2θ)*〔1-cos^2θ÷cos(90°-θ)〕列式

Some brackets are probably missing; please check and re-write the whole thing.
For example cosθ÷1 = cosθ. What does the symbol * mean?


Question 2: 求直綫L:3x-2y=12的斜率 列式

3x – 12 = 2y
2y = 3x -12
y = 3/2 x – 16
The slope is 3/2, 56.31 ° with the horizontal
(Sorry I don’t know what 斜率 in English.)


Question 3: 計算tan5°tan15°tan25°tan35°tan45°tan55°tan65°tan75°tan85° 列式

Rearrange them in this order
tan5°tan85°tan15 °tan75°tan25°tan65° tan35 tan55° tan45°
Put in brackets
(tan5°tan85°) (tan15 °tan75°) (tan25°tan65°) ( tan35 tan55°) tan45°
(1)(1) (1) (1) 1 = 1

Note : tan A tan B = 1 if angle A + angle B = 90°and tan 45°= 1
e.g. tan30° tan60°= 1/[sq. root(3) ] x sq. root (3) = 1
  tan45° tan45°= 1 x 1 = 1
tan A = side a/side b, if B = (90°- A), tan B = side b/side a, 
tan A x tan B = (side a/side b) (side b/side a) = 1


Question 4 :簡化(x-1) ÷〔x^2-(x+1)(x-1)〕
 
(x – 1)
------------------------- 
x^2 – (x+1)(x - 1)

(x – 1)
--------------------- 
x^2 – (x^2 – 1)

(x – 1)
------------------- 
x^2 – x^2 + 1

(x – 1)
---------  
+ 1

x + 1


Question 5: 39996÷(39999^2-39998×40000)

39996
----------------------------------- 
(39999^2-39998×40000)

39996
------------------------------------------------------------------ 
(39998 + 1) (3998 +1) – [39998 x (39998 +2)]

39996
--------------------------------------------------------------------------- 
(39998^2 + 2x3998 +1 – [39998x39998 +2x39998]

39996
------------------------------------------------------------------ 
(39998^2 + 2x3998 +1 – [39998^2 +2x39998]

39996
--------------------------------------------------------------- 
(39998^2 + 2x3998 +1 – 39998^2 - 2x39998

39996
---------  
+1

39996