Lines - GMAT Quantitative

The lines of the two equations must have slopes that are the opposites of each others reciprocals.

Write each equation in slope-intercept form:

As can be seen, knowing the value of is necessary and sufficient to answer the question. The value of is irrelevant.

The answer is that Statement 1 alone is sufficient to answer the question, but Statement 2 alone is not sufficient to answer the question.

To determine if two lines are perpendicular, only the slope needs to be considered. The slopes of perpendicular lines are the negative reciprocals of each other. Knowing a single point on the line is not sufficient, as an infinite number of lines can pass through and individual point.

Statement 1 alone establishes by definition that , but does not establish any relationship between and .

By Statement 2 alone, since alternating interior angles are congruent, , but no conclusion can be drawn about the relationship of , since the actual measures of the angles are not given.

Assume both statements are true. By Statement 2, . and are corresponding angles formed by a transversal across parallel lines, so . is not a right angle, so .

Statement 1 alone establishes nothing about the angle makes with , as it is not part of the triangle. Statement 2 alone only establishes that .

Assume both statements are true. Then is an altitude of an equilateral triangle, making it - and - perpendicular with the base - and .

Assume Statement 1 alone. The measure of one of the angles formed is

degrees.

Assume Statement 2 alone.

By substituting for , one angle measure becomes

The marked angles are a linear pair and thus their angle measures add up to 180 degrees; therefore, we can set up an equation:

or

yields illegal angle measures - for example,

yields angle measures for both angles; the angles are right and the lines are perpendicular.

To find the equation of a perpendicular line you need the slope of the line and a point on the line. We can find the slope by knowing g(x).

I) Gives us a point on h(x).

II) Gives us the y-intercept of h(x).

Either of these will be sufficient to find the rest of our equation.

Statement 1 allows you to define the equation of line m, but does not provide enough information to solve for . There are still 3 variables and only two different equations to solve.

if , statement 2 supplies enough information to solve for b by substitution if is on the line.

Consider linear functions h(t) and g(t).

I) at the point

II)

Is the point on the line h(t)?

We can use II) and I) to find the slope of h(t)

Recall that perpendicular lines have opposite reciprocal slope. Thus, the slope of h(t) must be

Next, we know that h(t) must pass through (6,4), so lets us that to find the y-intercept:

Next, check if (10,4) is on h(t) by plugging it in.

So, the point is not on the line, and we needed both statements to know.

To find the equation of any line, we need 2 pieces of information, the slope of the line and any point on the line. From statement 1, we get a point on Line AB. From statement 2, we get the slope of Line BC. Since we know that AB is perpindicular to BC, we can derive the slope of AB from the slope of BC. Therefore to find the equation of the line, we need the information from both statements.

Given the other endpoint, you can use the distance formula to find the length of the segment:

Given the midpoint, you can use the distance formula to find the distance from the first endpoint to the midpoint, then double that to get the length of the segment:

The total length is twice that, or 10.

The answer is that either statement alone is sufficient to answer the question.

If you know only that , then you know that and , but you still need , or a way finding it.

If you know only that , you still know only that , but you don't know their actual lengths.

If you know both facts, then you know

Statement I gives us a point.

Statement II gives us the length of the segment.

We are asked to find the coordinates of the other end of the segment. However, we will need more information. Even with all of our information, we have no clue as to the orientation of the line. It could be 14 units straight up and down, it could be a perfectly horizontal line, or something inbetween, thus our answer is:

Neither I nor II are sufficient to answer the question. More information is needed.

To find the length of a segment, use the distance formula. The distance formula is given by the following:

Where your 's and 's correspond to the coordinates of the endpoints.

To find the length of Segment YZ, we need the endpoints.

Statement I gives you Point Y's coordinates.

Statement II relates Point Z's coordinates to Point Y's coordinates. Thus, we can find the point Z using Statement II.

Therefore, we need both.

Recap:

Find the length of Segment YZ

I) Point Y is located at the point .

II) Point Z has a y-coordinate twice that of Point Y, and an x-coordinate one-third of Point Y.

Use Statement II along with Statement I to find the coordinates of Point Z:

Then, use distance formula to find the length of Segment YZ:

To find the length of a segment, we need both endpoints.

Statement I gives us one endpoint.

Statement II relates and , allowing us to find the second endpoint.

Thus, we need both. Once we have both endpoints, distance is easily calculated via the distance formula or the Pythagorean theorem.

Using Statement II, we find the second endpoint to be . Use the distance formula to find your answer:

Statement 1: Since the line we're looking for is perpendicular to line XY, our slope will be the inverse of line XY's slope .

The slope of our line is then . Just knowing the slope however, is not sufficient information to answer the question.

Statement 2: We're provided with a point which will allow us the write the equation.

Statement 1: We're given the equation to line AB which contains the slope. Because the line we're being asked for is perpendicular to it, we know the slope will be its inverse.

The slope of our line is then

Statement 2: We can write the equation to the perpendicular line only if we have a point that falls within that line. Luckily, we're given such a point in statement 2.

Both statements taken together are sufficient to answer the question, but neither statement alone is sufficient.

Find the equation of the line perpendicular to r(x)

I) r(x) has a slope of -15

II) The line must pass through the point (9, 96)

Recall that perpendicular lines have opposite reciprocal slopes.

Use I) to find the slope of our new line

Use II) along with our slope to find the y-intercept of our new line.

Therefore both statements are needed.

Recall that perpendicular lines have opposite, reciprocal slopes. We can find the slope of from the question.

Statement I gives us a point on , which we can use to find the y-intercept of , and then the equation.

The slope of must be the opposite reciprocal of , this makes our slope .

Statement I tells us that passes through the point , so we can use slope-intercept form to find our equation:

So, our equation is

Statement II gives us a point on , which does not help us in the slightest with . Therefore, only Statement I is sufficient.

Assume Statement 1 alone. The -intercept of the line of the equation can be found by substituting and solving for :

The -intercept of the line is the origin ; it follows that this is also the -intercept.

Therefore, Statement 1 alone yields only one point of the line, from which its equation cannot be determined.

Assume Statement 2 alone. The slope of the line of the equation can be calculated by putting it in slope-intercept form :

The slope of this line is the coefficient of , which is . A line perpendicular to this one has as its slope the opposite of the reciprocal of , which is

.

However, there are infintely many lines with this slope, so no further information can be determined.

Now assume both statements to be true. From Statement 1, the slope of the line is , and from Statement 2, the -coordinate of the -initercept is . Substitute in the slope-intercept form: