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In the rectangular coordinate system, what is the area of [#permalink]
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19 Dec 2007, 12:00
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In the rectangular coordinate system, what is the area of triangle PQR with points Q=(0,3) R=(7,4) P(4,0) A. 12.5 B. 14 C. 10 D. 16 E. 25
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Last edited by Bunuel on 17 Feb 2014, 07:19, edited 1 time in total.
Renamed the topic, edited the question, added the OA and moved to PS forum.



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Re: Geometry in coordinate plane [#permalink]
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19 Dec 2007, 12:38
mbsnyc wrote: In the rectangular coordinate system, what is the area of triangle PQR with points
Q=(0,3) R=(7,4) P(4,0)
a. 12.5 b. 14 c. 10 d. 16 e. 25
A
plot the points
make a square
subtract all the unnecessary triangles around the plotted triangle.
anyone know a faster way to do this?



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Re: Geometry in coordinate plane [#permalink]
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19 Dec 2007, 12:41
bmwhype2 wrote: mbsnyc wrote: In the rectangular coordinate system, what is the area of triangle PQR with points
Q=(0,3) R=(7,4) P(4,0)
a. 12.5 b. 14 c. 10 d. 16 e. 25 A plot the points make a square subtract all the unnecessary triangles around the plotted triangle. anyone know a faster way to do this?
use distance formula for each of the sides.
sides are 5 5 7
an isos rt triangle.
bh/2 = 5*5 / 2 = 12.5



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Re: Geometry in coordinate plane [#permalink]
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19 Dec 2007, 12:45
How did you know it was a right triangle and not just isc?



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Re: Geometry in coordinate plane [#permalink]
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19 Dec 2007, 12:45
bmwhype2 wrote: plot the points subtract all the unnecessary triangles around the plotted triangle.
The same way
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Re: Geometry in coordinate plane [#permalink]
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19 Dec 2007, 12:53
mbsnyc wrote: How did you know it was a right triangle and not just isc?
you're right. its simply an isosceles triangle. we can infer the height is 7 but im not sure how to get the base.



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Re: Geometry in coordinate plane [#permalink]
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19 Dec 2007, 14:00
mbsnyc wrote: In the rectangular coordinate system, what is the area of triangle PQR with points
Q=(0,3) R=(7,4) P(4,0)
a. 12.5 b. 14 c. 10 d. 16 e. 25
I get A.
Using the distance formula I get sides 5,5, 7
5*5/2=12.5



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Re: Geometry in coordinate plane [#permalink]
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05 May 2008, 18:57
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The area of a triangle with coordinates (x1,y1), (x2,y2), (x3,y3) is
1/2x1(y2y3)+x2(y3y1)+x3(y1y2)



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Re: In the rectangular coordinate system, what is the area of [#permalink]
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14 Feb 2014, 11:03
can we do this by distance formula.. square root (x2x1)^2+(y2y1)^2 I did that by this formula.. M geting 5, 5 and square root 50 respectively of three sides... so 5*5/2=12.5 Ans A. is it rite? whats another aproach?
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Re: In the rectangular coordinate system, what is the area of [#permalink]
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15 Feb 2014, 01:05
sanjoo wrote: can we do this by distance formula..
square root (x2x1)^2+(y2y1)^2
I did that by this formula.. M geting 5, 5 and square root 50 respectively of three sides... so 5*5/2=12.5 Ans A.
is it rite? whats another aproach? Yes you can do it with this formula... simplest and fastest approach. There are other approaches mentioned in the posts but those involve more steps. Like plotting a trapezium finding its area and then subtracting two 345 rt angled triangles to get the desired area.



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Re: In the rectangular coordinate system, what is the area of [#permalink]
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16 Feb 2014, 10:15
http://www.mathopenref.com/coordtrianglearea.html
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Re: In the rectangular coordinate system, what is the area of [#permalink]
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09 Nov 2014, 22:50
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To figure out if it's a right triangle we should figure out if two of the sides are vertical to each other.
side 1 coordinates are 0,3 and 4,0 => slope = 3/4 side 2 coordinates are 4,0 and 7,4 => slope = 4/3
slope side1 / slope side2 = (3/4)/(4/3) = 1 sides are perpendicular to each other and the triangle is right.
Now you can calculate side1 = 5 side2 = 5 area = (side1 x side2) / 2 = 12.5



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Re: In the rectangular coordinate system, what is the area of [#permalink]
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10 Nov 2014, 01:33
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we should count all three sides of PQR, so we get
5,5,5*sqrt2, meaning it is right triangle with 45, 45, 90 degree angles
so we only need to 5*5/2=12.5
A



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Re: In the rectangular coordinate system, what is the area of [#permalink]
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29 Dec 2015, 13:48
Adding to the diagram by walker, if once calculates the area of the triangle that has QR as the hypotenuse, it comes to be a noninteger, which subtracted from a whole integer (28) would give a non integer. The only non integer options is A
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Re: In the rectangular coordinate system, what is the area of
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