Math, asked by anshul348567890, 10 months ago

cosA=-3/5, pi<=A,=3pi/2 find sin2A

Answers

Answered by SparklingBoy
3

Answer:

Given that cosA=-3/5

and

 \pi  \leqslant A  &lt; \frac{3 \pi}{2}  \\  \implies \: A \: lies \: in \: 3rd \: quadrant

As ,

sin^{2}  A \:   + cos {}^{2} A = 1 \\  \implies \: ( \frac{ - 3}{5}) ^{2}  + sin {}^{2} A = 1 \\  \implies \: sin {}^{2} A =  \frac{16}{25}  \\ \implies \:  sinA =  \pm  \frac{4}{5}

As x € 3rd quadrant

⟹ only cot and tan will be positive and other trigonometric ratios will be negative hence SinA will be negative.

So,

sinA =  \frac{ - 4}{5}

Now using formula

sin2A = 2sinAcosA

sin2A = 2 \times   \frac{ - 4}{5}  \times  \frac{ - 3}{5}  \\  =  \frac{24}{25}

Answered by Anonymous
10

\underline{\green{\textsf{Answer:-}}}

\pink{\boxed{\blue{sin2A = \dfrac{24}{25}}}}

\underline{\green{\textsf{Explanation:-}}}

Given

cosA = \dfrac{-3}{5}

where,

\pi ≤ A ≤ \dfrac{3 \pi}{2}

•°• A is in Q-lll

To Find:

sin2A

Solution

From Pythagoras theorem

Hypoteneuse² = Adj. side² + Opp. side²

5² = 3² + x²

x² = 5²-3²

x² = 25-9

x = √16

x = 4

Opp. side = 4

sinA = \dfrac{opp.side}{Hypoteneuse}

sinA = \dfrac{-4}{5}

Since, A is in Q-lll

["sin " is negative]

w.k.t,

\boxed{sin2A = 2 sinA \: cosA}

sin2A = 2 \times \dfrac{-4}{5} \times \dfrac{-3}{5}

sin2A = 2 \times \dfrac{12}{25}

\blue{\boxed{\red{\green{sin\orange{2} \pink{A} }= \dfrac{24}{\blue{25}}}}}

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