## What is the direction angle of a vector?

The direction of a vector is the measure of the angle it makes with a horizontal line . tanθ=y2 ‘ y1x2 ‘ x1 , where (x1,y1) is the initial point and (x2,y2) is the terminal point.

**When can the resultant of two vectors be zero?**

Yes, two vectors of equal magnitude that are pointing in opposite directions will sum to zero. Two vectors of unequal magnitude can never sum to zero. If they point along the same line, since their magnitudes are different, the sum will not be zero.

**How do you know if two vectors are the same line?**

First, look at the direction vectors of both lines: r′1(t)=⟨3,1,’3⟩ and r′2(s)=⟨’6,’2,6⟩. Since these vectors differ by a scalar multiple, they are parallel. This means both lines “go” in the same direction. Thus the lines are either parallel or the same line (with different parametrizations).

### How do you know if two vectors are skew?

Skew lines in 3 dimensions are those which are not parallel and do not intersect. First we need to show that they are not parallel. To do this we take the direction vectors (the second part with λ or µ constats) and check that one is not a multiple of the other.

**How do you prove two vectors are parallel?**

Two vectors are parallel if they are scalar multiples of one another. If u and v are two non-zero vectors and u = cv, then u and v are parallel.

**Can vectors be skew?**

Since their direction vectors are not parallel, the two lines either intersect at a single point or are skew to each other.

Here’s the summary of our methods:

**How do you prove intersecting lines?**

Whenever you have two lines, only one of three things can happen: Either they are the same line, they are parallel lines, or the two lines intersect at a point. If the two lines intersect at a point, the vertical angles formed are congruent….Geometry.

**What do we call the two lines that never meet?**

parallel lines

## How many common points can be formed if two lines intersect?

Intersecting lines can never share a common point. Two intersecting lines can sometimes two points of intersection. Intersecting lines are noncoplanar lines that meet at one point. Two intersecting lines can form two pairs of vertical angles.

**What do parallel lines prove?**

If two lines are cut by a transversal and the alternate exterior angles are equal, then the two lines are parallel. Angles can be equal or congruent; you can replace the word “equal” in both theorems with “congruent” without affecting the theorem. So if ∠B and ∠L are equal (or congruent), the lines are parallel.

**What are three styles of proof?**

There are many different ways to go about proving something, we’ll discuss 3 methods: direct proof, proof by contradiction, proof by induction. We’ll talk about what each of these proofs are, when and how they’re used.

### What is the parallel lines theorem?

If two parallel lines are cut by a transversal, then corresponding angles are congruent. If two lines are cut by a transversal and corresponding angles are congruent, then the lines are parallel.

**What is transversal theorem?**

In geometry, a transversal is a line that passes through two lines in the same plane at two distinct points. As a consequence of Euclid’s parallel postulate, if the two lines are parallel, consecutive interior angles are supplementary, corresponding angles are equal, and alternate angles are equal.

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