tolong dbantu kumohon

2) cot A × sin A = cos A
=> (cos A/sin A) × sin A = cos A
=> cos A = cos A (terbukti)

3) [(1 - tan^2○)/(1 + tan^2 ○) = cos^2 ○ - sin^2 ○



cos^2 ○....sin^2 ○
----------- - --------------
cos^2 ○.....cos^2 ○
_______________ = cos^2 ○ - sin^2 ○
cos^2 ○......sin^2 ○
------------ + -------------
cos^2 ○.......cos^2 ○

cos^2 ○ - sin^2 ○
--------------------------
..........cos^2 ○
_____________ = cos^2 ○ - sin^2 ○
cos^2 ○ + sin^2 ○
----------------------------
...............cos^2 ○

cos^2 ○ - sin^2 ○.............cos^2 ○
-------------------------- ×--------------------------
.............cos^2 ○............cos^2○ + sin^2 ○
= cos^2 ○ - sin^2 ○

cos^2 ○ - sin^2 ○
------------------------- = cos^2 ○ - sin^2 ○
cos^2 ○ + sin^2 ○

cos^2 ○ - sin^2 ○
-------------------------- = cos^2 ○ - sin^2 ○
.................1

cos^2 ○ - sin^2 ○ = cos^2 ○ - sin^2 ○
(Terbukti)

4)sec^2 A × cosA
-------------------------- = tan A
..........cosec A

....1
------------ × cos A
cos^2 A
----------------------------- = tan A
..........1
---------------
....sin A

....1
----------
cos A
-------------- = tan A
......1
--------------
.......sin A

....1
-------- x sin A = tan A
cos A

sin A
---------- = tan A
cos A

tan A = tan A (Terbukti)