Big Ideas Math Geometry, 2014
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Big Ideas Math Geometry, 2014 View details
8. Coordinate Proofs
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Exercise 4 Page 285

What do point O and point J have in common? How about H and J?

Right triangle?: Yes
Side lengths: OM=m, HM=n, OH=sqrt(m^2+n^2)
Midpoints: M_(OM)( m2,0), M_(HM)(m, n2), M_(OH)( m2, n2)

Practice makes perfect

Is â–ł OHJ a right triangle?

The only point where we know both coordinates is O(0,0). Let's start by plotting this point.

Additionally, we know that J(m, 0) is on the x-axis because it's y-coordinate is 0. Let's mark this point as well. Since both O and M are on the same y-coordinate, the side between these points will be horizontal.

As for the third point, H( m,n), we know it's on the same x-coordinate as J( m,n). Therefore, HM will be a vertical side. Since the triangle has one vertical side and one horizontal side, this is in fact a right triangle.

Side lengths

To find the length of any side in a coordinate plane, we can use the Distance Formula. However, for vertical or horizontal sides, the formula is not necessary when calculating the length:

  • Horizontal segments: The length of a vertical segment is the absolute value of the difference between the endpoints' x-coordinates.
  • Vertical segments: The length of a vertical segment is the absolute value of the difference between the endpoints' y-coordinates.

Using this, we can find OM and HM

To determine the length of the last side, we have to use the Distance Formula.
d=sqrt((x_2-x_1)^2+(y_2-y_1)^2)
d_(OH)=sqrt(( m- 0)^2+( n- 0)^2)
d_(OH)=sqrt(m^2+n^2)
Let's summarize the side lengths: OM=m, HM=n, OH=sqrt(m^2+n^2)

Midpoints

By the definition of a midpoint, we know that such a point bisects each of the three sides. To find the midpoint of any side we can use the Midpoint Formula.

Side Points M(x_1+x_2/2,y_1+y_2/2) Midpoint
OM ( m,0), ( 0,0) M(m+ 0/2,0+ 0/2) M(m/2,0)
HM ( m,n), ( m,0) M(m+ m/2,n+ 0/2) M(m,n/2)
OH ( m,n), ( 0,0) M(m+ 0/2,n+ 0/2) M(m/2,n/2)

Let's summarize the midpoints: M_(OM)(m/2,0), M_(HM)(m,n/2), M_(OH)(m/2,n/2)