No, 2/5-3/4 is -7/20 and 1/4+2/5 is 13/20 they do not equal the same the so the answer is no because it’s not true
That depends. If you have a finite data set, you would add up all the points you have and divide by the total count.
Or, if you are working with pure distributions, the mean is the same as the expected value of the corresponding random variable.
Suppose you have a discrete random variable

with a given probability mass function

, then the mean is given by

which would mean you take all the possible probability for the event that

, multiply each by that

, and add them together.
If the distribution is continuous, say a random variable

that has probability distribution function

over some support

, then the mean is
<span>x - y = 30
therefore if y is 15
x - 15 = 30
so it follows that
x = 30 + 15
which means x has a value of 45x - y = 30
therefore if y is 15
x - 15 = 30
so it follows that
x = 30 + 15
which means x has a value of 45</span>
Its (1,-3) simply reflect it above the y-axis, if one vertex is on the negative side and the symmetry if about the y axis (y=0) therefore the reflection means the x value becomes inverse -1 changes to 1 and -3 remains the same