Coordinate Geometry
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ACT Math › Coordinate Geometry

What is the measurement of ?
Explanation
Whenever you have an angle that is inscribed to the outside edge of a circle and to an angle that passes through the midpoint of the circle, the inscribed angle will always be one half the measurement of the angle that passes through the midpoint of the circle.
Since the angle that passes through the midpoint of the circle is a straight angle (all straight angles measure  degrees), the inscribed angle must measure 
 degrees.

Since the sum of the internal angles of all triangles add up to  degrees, add up the measurements of the angles that you know and subtract the sum from 
 degrees to find your answer:
The coordinates of the endpoints of , in the standard 
 coordinate plane, are 
 and 
. What is the 
-coordinate of the midpoint of 
?
Explanation
To answer this question, we need to find the midpoint of .
To find how far the midpoint of a line is from each end, we use the following equation:
 and 
 are taken from the 
 value of the second point and 
 and 
 are taken from the 
 value of the first point. Therefore, for this data:
We can then solve:
Therefore, our midpoint is  units between each endpoint's 
 value and 
 unit between each endpoint's 
 value. To find out the location of the midpoint, we subtract the midpoint distance from the 
 point. (In this case it's the point 
.) Therefore:
So the midpoint is located at 
The question asked us what the -coordinate of this point was. Therefore, our answer is 
.
A deer walks in a straight line for 8 hours. At the end of its journey, the deer is 30 miles north and 40 miles east of where it began. What was the average speed of the deer?
 miles per hour
 miles per hour
 miles per hour
 miles per hour
 miles per hour
Explanation
To find the speed of the deer, you must have the distance traveled and the time.
The distance is found using the Pythagorean Theorem:
The answer must be in miles per hour so the total miles are divided by the hours to get the final answer:

What is the measurement of ?
Explanation
If you extend the lines of the parellelogram, you will notice that a parellogram is the same as 2 different sets of parellel lines intersecting one another. When that happens, the following angles are congruent to one another:

Therefore, 
Which point satisfies the system  and 
None of the other answers
Explanation
In order to solve this problem, we need to find a point that will satisfy both equations. In order to do this, we need to combine the two equations into a single expression. For this, we need to isolate either x or y in one of the equations. Since the equation  already has y isolated, we will use this equation. Next we substitue this equation into the first one. 
 becomes 
which simplifies to 
. Now we can solve for x by factoring: 
 Thus, 
.
Now that we have two possible values for x, we can plug each value into either equation to obtain two values for y. For  and the second equation, we get 
. Therefore our first point is 
. This is not one of the listed answers, so we will use our other value of x. For 
 and the second equation, we get 
. This gives us the point 
, which is one of the possible answers.
Find the distance between the points  and 
.
Explanation
The easiest way to find the distance between two points whose coordinates are given in the form  and 
 is to use the distance formula.
Plugging in the coordinates from our given points, our formula looks as follows
We then simply simplify step by step
Therefore, the distance between the two points is 13.
Which of the following is the slope-intercept form of ?
Explanation
To answer this question, we must put the equation into slope-intercept form, meaning we must solve for . Slope-intercept form follows the format 
 where 
 is the slope and 
 is the intercept.
Therefore, we must solve the equation so that  is by itself. First we add 
 to both sides so that we can start to get 
 by itself:
Then, we must subtract  from both sides:
We then must divide each side by 
Therefore, the slope-intercept form of the original equation is .
What is the midpoint between the points  and 
?
Explanation
To find the midpoint, find the midpoint (or just average) for the x and y value separately. For the x-value, this means: . For the y-value, this means: 
. Thus, the midpoint is (3,4).
What is the slope of the line given by the equation ?
Explanation
To find the slope, put the line in slope intercept form. In other words put the equation in  form where 
 represents the slope and 
 represents the y-intercept.
From here we can see our slope equals :
Find the distance between  and 
None of the other answers
Explanation
The expression used in solving this question is the distance formula: 
This formula is simply a variation of the Pythagorian Theorem. A great way to remember this formula is to visualize a right triangle where two of the vertices are the points given in the problem statement. For this question: 
Where a =  and b = 
. Now it should be easy to see how the distance formula is simply a variation of the Pythagorean Theorem.
We almost have all of the information we need to solve the problem, but we still need to find the coordinates of the triangle at the right angle. This can be done by simply taking the y-coordinate of the first point and the x-coordinate of the second point, resulting in .
Now we can simply plug and chug using the distance formula.