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jxharmon

Member

Registered: 2007-01-08

Posts: 104

2 equations=parallel lines

Determine which two equations represent parallel lines.
(a)  y = –2x + 2    (b)  y = 2x + 2    (c)  y =  x + 2
(d)  y = –2x + 5

luca-deltodesco

Member

Registered: 2006-05-05

Posts: 1,470

Re: 2 equations=parallel lines

lines are parallel when their gradients are equal. you should be able to work it out from there.

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jxharmon

Member

Registered: 2007-01-08

Posts: 104

Re: 2 equations=parallel lines

So I show y=2x+2 & y=1/2x+2 are parrallel...is that correct?

mathsyperson

Moderator

Registered: 2005-06-22

Posts: 4,900

Re: 2 equations=parallel lines

No, sorry. As luca says, lines are parallel when their gradients are equal. The gradient is given by the coefficient before the x term in the line's equation.

So, as the first of your lines has an equation of y = -2x + 2, then its gradient is -2.

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Stanley_Marsh

Member

Registered: 2006-12-13

Posts: 345

Re: 2 equations=parallel lines

slope same , intercept different

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jxharmon

Member

Registered: 2007-01-08

Posts: 104

Re: 2 equations=parallel lines

so it would be y=-2x+2 and y=2x+2; right

Last edited by jxharmon (2007-01-26 15:43:13)

mathsyperson

Moderator

Registered: 2005-06-22

Posts: 4,900

Re: 2 equations=parallel lines

Still no, I'm afraid. The gradients of those are -2 and 2 respectively, so they're not parallel.

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Why did the vector cross the road?
It wanted to be normal.

freddogtgj

Member

Registered: 2006-12-02

Posts: 54

Re: 2 equations=parallel lines

(a) and (d)
Am i right?

Toast

Real Member

Registered: 2006-10-08

Posts: 1,321

Re: 2 equations=parallel lines

Yep, the coefficients of x are both -2, so they must be parallel