# Painless Trigonometry

Sine of A

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

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

2. Arsh Singh. yourmathguru.com. 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

### Dan

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.

### 6 Responses

1. -84/25

2. kryptonj123 says:

3. kryptonj123 says:

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

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