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line p in the x-axis

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line p in the x-axis

by sanju09 » Sat Jul 24, 2010 1:54 am
If the equation of a line p in the coordinate plane is y = 3 x + 2, what is the equation of line q which is a reflection of line p in the x-axis?
A. y = -3 x + 2
B. y = -3 x - 2
C. y = 3 x - 2
D. y = -1/3 x - 5
E. y = -1/3 x + 5
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by selango » Sat Jul 24, 2010 2:02 am
y=3x+2

(x,y)=(-2/3,2)

Relection in x axis (2/3,2)

y=-3x+2

Pick A
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by Hussain15 » Sat Jul 24, 2010 4:50 am
"C" is my pick. Whats the OA??
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by sanju09 » Sat Jul 24, 2010 5:35 am
Hussain15 wrote:"C" is my pick. Whats the OA??

When it came to me, I assumed a line with its rise being 3 times as much as its run and the intercept on y-axis being 2 in positive.

When a line is reflected in the x-axis, its intercept on y-axis changes sign only, eliminate A, D, and E; but the intercept on x-axis remains same. This must result in the slope also changing sign only. Now pick B
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by selango » Sat Jul 24, 2010 6:08 am
Sanju,

If the line is reflected on x axis,it either in first or second quadrant..right?

Here the line is in 1st quadrant.Then the reflection must be in 2nd quadrant.

Pls clarify.
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by sanju09 » Sat Jul 24, 2010 6:18 am
selango wrote:Sanju,

If the line is reflected on x axis,it either in first or second quadrant..right?

Here the line is in 1st quadrant.Then the reflection must be in 2nd quadrant.

Pls clarify.

How can we call a line to be limited to any quadrant, it's the point that could be in any quadrant. A line is free to trespass the borders called the axes.

Try to draw out what I said in the above post, on a rectangular plane, creep through the choices to eliminate few, ask for graphics if doubt remains.
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by selango » Sat Jul 24, 2010 6:21 am
sanju09 wrote:
selango wrote:Sanju,

If the line is reflected on x axis,it either in first or second quadrant..right?

Here the line is in 1st quadrant.Then the reflection must be in 2nd quadrant.

Pls clarify.

How can we call a line to be limited to any quadrant, it's the point that could be in any quadrant. A line is free to trespass the borders called the axes.

Try to draw out what I said in the above post, on a rectangular plane, creep through the choices to eliminate few, ask for graphics if doubt remains.
Can you please explain this with a diagram.

The line y=3x+2 is in second quadrant..rt?
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by sanju09 » Sat Jul 24, 2010 6:23 am
selango wrote:
sanju09 wrote:
selango wrote:Sanju,

If the line is reflected on x axis,it either in first or second quadrant..right?

Here the line is in 1st quadrant.Then the reflection must be in 2nd quadrant.

Pls clarify.

How can we call a line to be limited to any quadrant, it's the point that could be in any quadrant. A line is free to trespass the borders called the axes.

Try to draw out what I said in the above post, on a rectangular plane, creep through the choices to eliminate few, ask for graphics if doubt remains.
Can you please explain this with a diagram.

The line y=3x+2 is in second quadrant..rt?
only a part of it is in the 2nd quadrant
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by outreach » Sat Jul 24, 2010 10:33 am
@selango

reflection in X axis means y value will have opposite sign
Reflection in x axis (-2/3,-2)

HENCE B Shd be the answer
selango wrote:y=3x+2

(x,y)=(-2/3,2)

Relection in x axis (2/3,2)

y=-3x+2

Pick A
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