x & y intercepts of 7x + y + 3 = y

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halokel

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Oct 29, 2008
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Need help with determining the x & y intercept for the following

7x+y + 3 = y
or
7x = -3

plugging in 0 for the y intercept is
7(0) = -3
(0,-3)

Confused about the x intercept since there is no y in the equation. Is the x intercept (0,0)?

Thank you.

halokel
 
Re: x & y intercepts

I assume you are studying straight lines.
so let us rewrite the equation in the form of y=mx+b

7x+y+3=y
subtract y from each side of = sign
7x+3=0 this is not a straight line . solve for x
subtract 3 from each side of = sign
7x=-3
divide each side of = sign by 7
x=-3/7 this is a point on the number line

There is no x or y intercepts with the axis, because we do not have a equation of a line

Arthura
 
Re: x & y intercepts

Thank you.. I understand what you did, but now we are confused whether or not an equation such as: x = -8 is a linear equation. My daughter's math teacher is telling the class x = 8 is not, but x = -8 is. We don't see the difference. We thought all linear equations were Ax + By = C and that it had to have 2 single variables (no squares or roots or something like 8xy as a variable). Pulling my hair out!

halokel
 
Re: x & y intercepts

halokel said:
Thank you.. I understand what you did, but now we are confused whether or not an equation such as: x = -8 is a linear equation. My daughter's math teacher is telling the class x = 8 is not,

x = 8 is a linear equation - the graph of this equation is a vertical straight line.

but x = -8 is. We don't see the difference. We thought all linear equations were Ax + By = C and that it had to have 2 single variables (no squares or roots or something like 8xy as a variable). Pulling my hair out!(Don't - save some for her college years)

halokel
Click to expand...
 
Re: x & y intercepts

I agree with your math instructor.

y=mx+b is a straight line or ax+by=c

equations containing square terms are conic sections,i.e. y^2=x, or x^2+y^2=r^2

x=8 is a point on the number line.
x=-8 is a point on the number line

Arthur
 
I have already said that 7x+y+3=y is not a straight line but a number on the number line
x=-3/7 a rational number. [a rational number is a number that can be expressed as a RATIO OF integers]

I believe the instructor gave the student a "trick" question. It appeared similiar to ax+by=c
but was actually x=C. I assume he gave the problem to see if the student really understood the equation of a straight line
Arthur
 
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