The y intercept of a line L is 4. If the slope of L is negative, which of the following could be the x intercept of L.

I. -1
II. 0
III. 6

A. I only
B. II only
C. III only
D. I and II
E. I and III

C) III only

The y-intercept is 4. Therefore we have y=mx+4

It is given that the slope is negative. Therefore the line must go from top left to bottom right.

i.e: the x-intercept has to be positive. That itself rules out I & II.

If you choose to go with the options directly, here's an approach.

y=mx+4. For the x-intercept, y=0.
i.e. mx+4=0.

We know that the slope m is negative. Therefore, if x=-1 or x=0, the equation mx+4 =0 would never be satisfied.

If x=6, we have 6m+4=0. A value of m=-2/3 would satisfy this equation.

Hope this helps.

said C, 3 only....got it down to x=4/m ... looked at the answers and only 6 fit.

Slope of the line x/a + y/b = 1 is -b/a here b = 4

hence slope = -4/a since -4/a is -ve, 'a' must be non zero and positive.
Only solution is 6

Thus C
_________________

Try visualizing the problem.

There are 2 givens:
1) The y intercept is 4
2) The slope is negative

Now draw out a coordinate plane and try to draw a few sample solutions that meet the above givens.

The only way the line can cross -1 is if the slope was positive. The line will also never cross 0 because that would form an undefined slope.

Solution 1) 6 is the only valid option. Therefore, the correct answer is C.

No. You are mixing it up.
the slope is negative
Hence you can write
y=(-m)x+4
since -m is negative, in this case m must be positive
again your slope is -m, not m!!

So later if you say mx=4
x is necessarily positive since m is positive.

Try to be rigorous when you create variables.

slope(Intercept form) = - y(intercept)/ x (intercept)
we are also given that slope should be negative.
we are told that "y intercept of a line L is 4".

s = -4/x;

x has to be positive to maintain a negative slope .

only option C satisfies.

Slope of a line = – (y intercept)/(x intercept)
Since slope is given to be negative, and y intercept is positive, we can say that x intercept must be positive too. So x intercept can be only III.

Answer (C)

For more on the slope formula, check:
http://www.veritasprep.com/blog/2011/09 ... -vertices/
_________________