Question

given: sin theta= 2/3 and theta is in the second quadrant; evaluate the following expression. sin2theta

Answer 1

The value of $\sin(2\theta)$ is $-\frac {-4\sqrt 3 }9$

Sine ratio

The sine ratio is given as:

$\sin(\theta) = \frac23$

Trigonometry

In trigonometry, we have the following ratio

$\sin^2(\theta) + \cos^2(\theta) = 1$

Substitute $\sin(\theta) = \frac23$ in the above equation

$\frac 23 + \cos^2(\theta) = 1$

Collect like terms

$\cos^2(\theta) = 1 -\frac 23$

Evaluate

$\cos^2(\theta) =\frac 13$

Take square roots

$\cos(\theta) =\pm\frac 1{\sqrt 3 }$

Rationalize

$\cos(\theta) =\pm\frac {\sqrt 3 }3$

From the question, $\theta$ is in the second quadrant, and cosine is negative.

So, we have:

$\cos(\theta) =-\frac {\sqrt 3 }3$

In trigonometry, we have:

$\sin(2\theta) = 2\sin(\theta)\cos(\theta)$

So, we have:

$\sin(2\theta) = 2\times \frac 23 \times -\frac {\sqrt 3 }3$

$\sin(2\theta) = -\frac {-4\sqrt 3 }9$

Hence, the value of $\sin(2\theta)$ is $-\frac {-4\sqrt 3 }9$

Read more about trigonometry ratios at:

brainly.com/question/10417664