Hi,
This is about Coordinate Geometry questions on GMAT. Can anyone help me?
Anybody experienced below type of questions on GMAT? Otherwise, can we expect them?
1. Find the area of the triangle ABC given A(6,7), B(2,-9) and C(-4, 1).
2. If the points (-1, 3), (b, -1), (0, 4) are on a line, find value of 'b'.
Regards
KB Devaraj
Coordinate Geometry questions on GMAT
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- sanju09
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kbdevaraj wrote:Hi,
This is about Coordinate Geometry questions on GMAT. Can anyone help me?
Anybody experienced below type of questions on GMAT? Otherwise, can we expect them?
1. Find the area of the triangle ABC given A(6,7), B(2,-9) and C(-4, 1).
2. If the points (-1, 3), (b, -1), (0, 4) are on a line, find value of 'b'.
Regards
KB Devaraj
Whenever GMAT asks the area of a triangle with the coordinates of its three vertices given, in most of the cases plotting the points on the rectangular axes helps us easily find one base and its corresponding altitude so that ½ b h formula can be used. But if it's not so, then dole out the coordinates of three vertices as (x1, y1), (x2, y2), and (x3, y3) and then use the following formula
∆ = ½ |x1 (y2 - y3) + x2 (y3 - y1) + x3 (y1 - y2)|
1. This way, A (6, 7), B (2, -9) and C (-4, 1) could give
∆ = ½ |6 (-9 - 1) + 2 (1 - 7) - 4 (7 + 9)|
= ½ |-60 - 12 - 64|
= ½ × 136 = [spoiler]68 units[/spoiler]
2. The concept of three points being collinear lies in the fact that no triangle can be formed using three points that are collinear, and if the area of a triangle whose three vertices are given collinear is calculated by using the above mentioned formula, then the result will be zero. See
When (-1, 3), (b, -1), (0, 4) are collinear
∆ = ½ |-1 (-1 - 4) + b (4 - 3) + 0 (3 + 1)| = 0
or, |5 + b + 0| = 0
or b = [spoiler]-5[/spoiler]
The mind is everything. What you think you become. -Lord Buddha
Sanjeev K Saxena
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Sanjeev K Saxena
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- HSPA
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Hi Sanju.. Kindly judge my approach
Calculate the base = lenght of BC = distance btw two point BC = sqrt(136)
Calculate the height = distance between point A to line BC
Line BC's equation is 5x+3y-17 = 0
distance of point A to above line = 5*6+3*7-17/sqrt(5^2+3^2) = sqrt(34)
Now area = 1/2*base*height = 1/2*sqrt(136)*sqrt(34) = 34 sq units
Calculate the base = lenght of BC = distance btw two point BC = sqrt(136)
Calculate the height = distance between point A to line BC
Line BC's equation is 5x+3y-17 = 0
distance of point A to above line = 5*6+3*7-17/sqrt(5^2+3^2) = sqrt(34)
Now area = 1/2*base*height = 1/2*sqrt(136)*sqrt(34) = 34 sq units
- sanju09
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yes you maykbdevaraj wrote:Thanks Sanju for the explanation.
But do we get these kind of question on gmat?
Devaraj
The mind is everything. What you think you become. -Lord Buddha
Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001
www.manyagroup.com
Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001
www.manyagroup.com
- sanju09
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This approach is not recommendable when easier and quicker approaches are already there. Your work is absolutely correct ACCEPT a calculation error towards the end (see BOLD above), I am getting the equation of line BC asHSPA wrote:Hi Sanju.. Kindly judge my approach
Calculate the base = lenght of BC = distance btw two point BC = sqrt(136)
Calculate the height = distance between point A to line BC
Line BC's equation is 5x+3y-17 = 0
distance of point A to above line = 5*6+3*7-17/sqrt(5^2+3^2) = sqrt(34)
Now area = 1/2*base*height = 1/2*sqrt(136)*sqrt(34) = 34 sq units
5 x + 3 y + 17 = 0
and this would get you the area as [spoiler]68[/spoiler] sq units
The mind is everything. What you think you become. -Lord Buddha
Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001
www.manyagroup.com
Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001
www.manyagroup.com
- GMATGuruNY
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1. Find the area of the triangle ABC given by A(6,7), B(2,-9) and C(-4, 1).
Use (-1,3) and (0,4) to determine the slope:2. If the points (-1, 3), (b, -1), (0, 4) are on a line, find the value of 'b'.
(4-3)/(0-(-1)) = 1/1 = 1.
Thus, (b,-1) and (0,4) must yield a slope of 1:
(b-0)/(-1-4) = 1
b/(-5) = 1.
b = -5.
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- HSPA
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First question: Thanks for the correction sanju...
For the second question.. My approach
three points are on same line.. so substitute the unknown point in the line equation formed using the other two points.
For the second question.. My approach
three points are on same line.. so substitute the unknown point in the line equation formed using the other two points.