Math  /  Geometry

QuestionFocus 1 Explain why vertically opposite angles are equal.

Studdy Solution

STEP 1

What is this asking? We need to explain why angles that are opposite each other, formed by two intersecting lines, are always equal. Watch out! Don't assume things just *look* equal!
We need a solid, logical argument backed by facts.

STEP 2

1. Set the Stage
2. Adjacent Angles
3. Opposite Angles

STEP 3

Let's imagine two lines intersecting each other.
Boom! Now, we've got four angles formed around the point where they cross.
Let's label these angles aa, bb, cc, and dd.
Visualize aa and bb together on one side of a line, then cc and dd together on the other side of that same line.
Then, aa and cc are opposite each other, and so are bb and dd.

STEP 4

Think about angles aa and bb.
They're right next to each other, sharing a line, making them **adjacent angles**.
What's special about adjacent angles formed by intersecting lines?
They add up to **180 degrees**, forming a straight line!
We can write this as: a+b=180a + b = 180

STEP 5

Now, let's look at angles cc and bb.
They're also adjacent angles!
So, just like aa and bb, they add up to **180 degrees**: c+b=180c + b = 180

STEP 6

We've got two equations now, both equal to **180**: a+b=180a + b = 180 and c+b=180c + b = 180.
Since they both equal the same thing, we can set them equal to each other: a+b=c+ba + b = c + b

STEP 7

Now, the magic happens!
Both sides of the equation have a bb.
We can subtract bb from both sides.
We're not "canceling" bb, we're adding b-b to both sides, and b+(b)=0b + (-b) = 0.
So, we get: a+bb=c+bba + b - b = c + b - b a+0=c+0a + 0 = c + 0a=ca = c

STEP 8

BAM! We just proved that angle aa is equal to angle cc.
These are our **vertically opposite angles**!
We could do the same thing for angles bb and dd to show they are equal too.

STEP 9

Vertically opposite angles are equal because they are supplementary to the same adjacent angle.
When we set those supplementary relationships equal to each other, we can then subtract the common adjacent angle from both sides, leaving us with the equality of the vertically opposite angles.

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