This is how I would do it, hope this helps!
The answer choice that correctly calculates and interprets the standard deviation of the sum, S = X + Y is D. Sigma Subscript s = 0.8; companies A and B can expect the total weight of packages to vary by approximately 0.8 ounces from the mean.
<h3>What does the standard deviation means?</h3>
A standard deviation means the all measure of how dispersed the data is in relation to the mean. It should be noted that low standard deviation means that the data are clustered around the mean, and the high standard deviation means that the data are more spread out.
In this case, the answer choice that correctly calculates and interprets the standard deviation of the sum, S = X + Y is the sigma Subscript s = 0.8; companies A and B can expect the total weight of packages to vary by approximately 0.8 ounces from the mean.
In conclusion, the correct option is D.
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First lets see the pythagorean identities

So if we have to solve for sin theta , first we move cos theta to left side and then take square root to both sides, that is

Now we need to check the sign of sin theta
First we have to remember the sign of sin, cos , tan in the quadrants. In first quadrant , all are positive. In second quadrant, only sin and cosine are positive. In third quadrant , only tan and cot are positive and in the last quadrant , only cos and sec are positive.
So if theta is in second quadrant, then we have to positive sign but if theta is in third or fourth quadrant, then we have to use negative sign .