Painless Trigonometry


Sine of A

Given      cosA=\displaystyle\frac{2}{5}.    What is sin2A if A is on the 4th quadrant?


Send your answer to or to our facebook page. Please do not forget to include your name and affiliated school or company. Use the category name as subject. Names of those who submitted the correct answer will be posted on this page immediately after the answer has been reviewed.

Correct answer were submitted by:

1. Nivlem Alas-as. MSEUF Lucena City. 4th Year High School

2. Arsh Singh. India

3. Kenny Wong, Jurong Junior College, Singapore

4.  Jerome Bechayda. Laguna State Polytechnic University,San Pablo City Campus

5. John Rey Jimenez. Negros Occidental High School.

6. Jomari Tan. DLSU

7.Sebastian Pineda Berrio. Colombia

8. Hrushikesh Bhope. St Xavier’s High School. India



Blogger and a Math enthusiast. Has no interest in Mathematics until MMC came. Aside from doing math, he also loves to travel and watch movies.

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5 Responses

  1. kryptonj123 says:

    Please review your solution

  2. kryptonj123 says:

    The correct answer for this problem is $latex \frac{-4\sqrt21}{25}$

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