Intermediate Geometry : Distance Formula

Study concepts, example questions & explanations for Intermediate Geometry

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Example Questions

Example Question #1 : How To Find The Length Of A Line With Distance Formula

A line segment begins from the origin and is 10 units long, which of the following points could NOT be an endpoint for the line segment?

Possible Answers:

\(\displaystyle (5,9)\)

\(\displaystyle (\sqrt{15},-\sqrt{85})\)

\(\displaystyle (6,8)\)

\(\displaystyle (7,\sqrt{51})\)

\(\displaystyle (-6,8)\)

Correct answer:

\(\displaystyle (5,9)\)

Explanation:

By the distance formula, the sum of the squares of each point must add up to 10 squared. The only point that doesn't fufill this requirement is (5,9)

Example Question #2 : How To Find The Length Of A Line With Distance Formula

A line segment is drawn starting from the origin and terminating at the point \(\displaystyle (15,8)\).  What is the length of the line segment?

Possible Answers:

\(\displaystyle \sqrt{264}\)

\(\displaystyle 17\)

\(\displaystyle \sqrt{285}\)

\(\displaystyle 16\)

\(\displaystyle 21\)

Correct answer:

\(\displaystyle 17\)

Explanation:

Using the distance formula, \(\displaystyle \sqrt{8^{2}+15^{2}} = 17\)

Example Question #3 : How To Find The Length Of A Line With Distance Formula

What is the distance between \(\displaystyle (-2,-3)\) and \(\displaystyle (6,12)\)?

Possible Answers:

\(\displaystyle 13\)

\(\displaystyle 19\)

\(\displaystyle 15\)

\(\displaystyle 11\)

\(\displaystyle 17\)

Correct answer:

\(\displaystyle 17\)

Explanation:

In general, the distance formula is given by:  \(\displaystyle d=\sqrt{(x_{2}-x_{1})^{2}+{(y_{2}-y_{1})^{2}}}\) and is based on the Pythagorean Theorem.

Let \(\displaystyle P_{1}=(-2,-3)\) and \(\displaystyle P_{2}= (6,12)\)

So the equation to soolve becomes \(\displaystyle d=\sqrt{(6-(-2))^{2}+{(12-(3))^{2}}}\) or \(\displaystyle d=17\)

 

Example Question #4 : How To Find The Length Of A Line With Distance Formula

If we graph the equation \(\displaystyle y=-2x+4\) what is the distance from the y-intercept to the x-intercept?

Possible Answers:

\(\displaystyle 2\sqrt{6}\)

\(\displaystyle \sqrt{6}\)

\(\displaystyle 20\)

\(\displaystyle \sqrt{5}\)

\(\displaystyle 2\sqrt{5}\)

Correct answer:

\(\displaystyle 2\sqrt{5}\)

Explanation:

First, you must figure out where the x and y intercepts lie. To do this we begin by plugging in \(\displaystyle y=0\) to our equation, giving us \(\displaystyle -2x+4=0\). Thus \(\displaystyle x=2\). So our x-intercept is the point \(\displaystyle (2,0)\). We then plug in \(\displaystyle x=0\), giving us \(\displaystyle y=4\), so we know our y-intercept is the point \(\displaystyle (0,4)\). We then use the distance formula \(\displaystyle d=\sqrt{(x_{1}-x_{2})^2+(y_{1}-y_{2})^2}\) and plug in our points, giving us \(\displaystyle d=\sqrt{(2-0)^2+(0-4)^2}=\sqrt{20}=2\sqrt{5}\)

Example Question #54 : Lines

Find the distance of the line connecting the pair of points

\(\displaystyle (0,0)\) and \(\displaystyle (5, 12)\).

Possible Answers:

\(\displaystyle 10\)

\(\displaystyle 13\)

\(\displaystyle 18\)

\(\displaystyle 15\)

Correct answer:

\(\displaystyle 13\)

Explanation:

By the distance formula 

\(\displaystyle \sqrt{(x_2-x_1)^2+(y_2-y_1)^2 }\)

where \(\displaystyle (x_1,y_1)=(0,0)\) and \(\displaystyle (x_2,y_2)=(5,12)\)

we have

\(\displaystyle \sqrt{(5-0)^2+(12-0)^2 }=\sqrt{(5)^2+(12)^2}= \sqrt{25+144} = \sqrt{169} = 13\)

Example Question #1 : How To Find The Length Of A Line With Distance Formula

Find the distance of the line connecting the pair of points

\(\displaystyle (1, 2)\) and \(\displaystyle (4, 6)\).

Possible Answers:

\(\displaystyle 3\)

\(\displaystyle 4\)

\(\displaystyle 5\)

\(\displaystyle 2\)

Correct answer:

\(\displaystyle 5\)

Explanation:

By the distance formula 

\(\displaystyle \sqrt{(x_2-x_1)^2+(y_2-y_1)^2 }\)

where \(\displaystyle (x_1,y_1)=(1,2)\) and \(\displaystyle (x_2,y_2)=(4,6)\)

we have

\(\displaystyle \sqrt{(4-1)^2+(6-2)^2 }=\sqrt{(3)^2+(4)^2}= \sqrt{9+16} = \sqrt{25} = 5\)

Example Question #1344 : Intermediate Geometry

Find the length of \(\displaystyle \small y = \frac{1}{5} x - 2\) for \(\displaystyle \small -2 \leq x \leq 5\)

Possible Answers:

\(\displaystyle \small \sqrt{9.36}\)

\(\displaystyle \small \sqrt{36.56}\)

\(\displaystyle \small \small \sqrt{60.56}\)

\(\displaystyle \small \small \sqrt{50.96}\)

\(\displaystyle \small \sqrt{26.96}\)

Correct answer:

\(\displaystyle \small \small \sqrt{50.96}\)

Explanation:

To find the distance, first we have to find the specific coordinate pairs that we're finding the distance between. We know the x-values, so to find the y-values we can plug these endpoint x-values into the line:

\(\displaystyle \small y = \frac{1}{5}(-2)-2\) first multiply

\(\displaystyle \small y = -0.4 - 2\) then subtract

\(\displaystyle \small y = -2.4\)

 

\(\displaystyle \small y = \frac{1}{5}(5)-2\) first multiply 

\(\displaystyle \small y = 1 - 2\) then subtract

\(\displaystyle \small y = -1\)

Now we know that we're finding the distance between the points \(\displaystyle \small \small (5, -1)\) and \(\displaystyle \small (-2, -2.4)\). We can just plug these values into the distance formula, using the first pair as \(\displaystyle \small (x_{1}, y_{1})\) and the second pair as \(\displaystyle \small (x_{2}, y_{2})\). It would work either way since we are squaring these values, this just makes it easier.

\(\displaystyle \small \sqrt{(x_{1}-x_{2})^2 + (y_{1}- y_{2})^2}\)

\(\displaystyle \small \sqrt{(5--2)^2 + (-1 - -2.4)^2 }\)

\(\displaystyle \small \sqrt{(5+2)^2 + (-1 + 2.4)^2}\)

\(\displaystyle \small \sqrt{7^2 + 1.4^2}\)

\(\displaystyle \small \sqrt{49+1.96} = \sqrt{50.96}\)

Example Question #1 : How To Find The Length Of A Line With Distance Formula

Find the length of \(\displaystyle \small y = -3x + 4\) for \(\displaystyle \small 0 \leq x \leq 5\)

Possible Answers:

\(\displaystyle 20\)

\(\displaystyle \small \small \sqrt{74}\)

\(\displaystyle 4\sqrt{17}\)

\(\displaystyle \small \sqrt{554}\)

\(\displaystyle 5\sqrt{10}\)

Correct answer:

\(\displaystyle 5\sqrt{10}\)

Explanation:

To find the distance, first we have to find the specific coordinate pairs that we're finding the distance between. We know the x-values, so to find the y-values we can plug these endpoint x-values into the line:

\(\displaystyle \small \small y = -3(0)+4\) first multiply

\(\displaystyle \small \small y = 0 +4\) then add

\(\displaystyle \small \small y = 4\)

 

\(\displaystyle \small \small y =-3(5)+4\) first multiply 

\(\displaystyle \small \small y = -15 +4\) then add

\(\displaystyle \small \small y = -11\)

Now we know that we're finding the distance between the points \(\displaystyle \small (0,4)\) and \(\displaystyle \small (5, -11)\). We can just plug these values into the distance formula, using the first pair as \(\displaystyle \small (x_{1}, y_{1})\) and the second pair as \(\displaystyle \small (x_{2}, y_{2})\). Note that it would work either way since we are squaring these values anyway.

\(\displaystyle \small \sqrt{(x_{1}-x_{2})^2 + (y_{1}- y_{2})^2}\)

\(\displaystyle \small \small \sqrt{(0-5)^2 + (4 - -11)^2 }\)

\(\displaystyle \small \small \sqrt{(-5)^2 + (15)^2}\)

\(\displaystyle \small \small \sqrt{25 + 225} = \sqrt{250}\)

Example Question #2 : How To Find The Length Of A Line With Distance Formula

Find the length of the line \(\displaystyle \small y= \frac{1}{2}x - 6\) for \(\displaystyle \small -1 \leq y \leq 8\)

Possible Answers:

\(\displaystyle \small \sqrt{137.25}\)

\(\displaystyle \small \sqrt{373}\)

\(\displaystyle \small \sqrt{481}\)

\(\displaystyle 9\sqrt{5}\)

\(\displaystyle \small \sqrt{733}\)

Correct answer:

\(\displaystyle 9\sqrt{5}\)

Explanation:

To find the distance, first we have to find the specific coordinate pairs that we're finding the distance between. We know the y-values, so to find the x-values we can plug these endpoint y-values into the line:

\(\displaystyle \small -1 = \frac{1}{2}x - 6\) add 6 to both sides

\(\displaystyle \small 5 = \frac{1}{2} x\) multiply by 2

\(\displaystyle 10 = x\) this endpoint is (10, -1)

 

\(\displaystyle \small 8 = \frac{1}{2} x -6\) add 6 to both sides

\(\displaystyle \small 14 = \frac{1}{2}x\) multiply by 2

\(\displaystyle \small 28 = x\) this endpoint is (28, 8)

 

Now we can plug these two endpoints into the distance formula:

\(\displaystyle \small \sqrt{(x_{1}- x_{2})^2 + (y_{1} - y_{2})^2 }\) note that it really does not matter which pair we use as \(\displaystyle \small (x_{1}, y_{1})\) and which as \(\displaystyle \small (x_{2}, y_{2})\) since we'll be squaring these differences anyway, just as long as we are consistent.

\(\displaystyle \small \sqrt{(28 - 10)^2 + (8 - - 1 )^2 }\)

\(\displaystyle \small \sqrt{18^2 + 9^2 }\)

\(\displaystyle \small \sqrt{324 + 81 } = \sqrt{405}=9\sqrt{5}\)

Example Question #61 : Lines

Find the length of \(\displaystyle y = \frac{1}{5} x + 7\) for the interval \(\displaystyle -5 \leq x \leq 10\).

Possible Answers:

\(\displaystyle 15.297\)

\(\displaystyle 15.033\)

\(\displaystyle 5.099\)

\(\displaystyle 16.155\)

\(\displaystyle 5.831\)

Correct answer:

\(\displaystyle 15.297\)

Explanation:

To find this length, we need to know the y-coordinates for the endpoints.

First, plug in -5 for x:

\(\displaystyle y = \frac{1}{5}(-5) + 7 = -1 + 7 = 6\)

Next, plug in 10 for x:

\(\displaystyle y = \frac{1}{5} (10 ) + 7 = 2 + 7 = 9\)

So we are finding the distance between the points \(\displaystyle (-5, 6)\) and \(\displaystyle (10, 9 )\)

We will use the distance formula, \(\displaystyle \sqrt{(x_1 - x_2)^2 + (y_1 - y_2 ) ^2 }\). We could assign either point as \(\displaystyle (x_1, y_1)\) and it would still work, but let's choose \(\displaystyle (10, 9 )\):

\(\displaystyle \sqrt{(10 - - 5 )^2 + (9 - 6 )^ 2 } = \sqrt{15^2 + 3^2 } = \sqrt{225 + 9 } = \sqrt{234} \approx 15.297\)

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