About Lesson
(1) Prove the following identities
证明下列恒等式
(a) 

(b) 

(c) 

(d) 

(e) 

(f) 

(g) 

(h) 

(i) 

(j) 

(2)
If ,
and
; find without using calculator or tables, the values of
若,
和
; 不用计算机或查表,求
(a)
(b)
(c)
Answer 答案:
(a) 
(b)
(c)

(b)

(c)

(3)
Given that
, find the values of a, b and c.
已知
, 求 a, b 和 c的值.
Given that

已知

Answer 答案:
,
,