Slope of line

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Slope of line

by gmattesttaker2 » Sat Nov 23, 2013 5:23 pm
Hello,

Can you please assist with this:

If AB > 0, then which of the following
must be true about line Ax + By + 5 = 0?

A) has positive slope
B) has negative slope
C) is horizontal
D) is vertical
E) passes through the origin of the xy-system

OA:B

I attempted to solve as follows: Ax + By + 5 = 0
=> By = -Ax - 5
=> y = (-A/B)x + (-5/B)

Now, A>0 and B>0 or A<0 and B<0

However, I am stuck after this point. Can you please assist?

Thanks,
Sri
Source: — Problem Solving |

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by Uva@90 » Sat Nov 23, 2013 6:00 pm
Sri,
What you did is Exactly correct.
As you know the line equation Y = mX+c

and what you derived is
y = (-A/B)x + (-5/B)
So, we can say m = -(A/B)
If M is negative then slope is negative.

hence line has Negative slope.

Answer is B

Regards,
Uva.
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by [email protected] » Sat Nov 23, 2013 8:09 pm
Hi Sri,

This question can be solved in number of ways; Since it has variables in it, you could TEST Values:

We know that AB > 0, so let's say:

A = 1
B = 1

So the given equation becomes X + Y + 5 = 0
Solving for Y gives us...

Y = -X + 5

Only answer B is correct. None of the others are true.

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