If [tex]\( G \)[/tex], [tex]\( D \)[/tex], and [tex]\( R \)[/tex] denote the number of grades, degrees, and radians respectively of an angle, prove that:

[tex]\[ \frac{G}{100} = \frac{D}{90} = \frac{2R}{\pi} \][/tex]



Answer :

Certainly! Let's prove the given relations step by step.

Given:
[tex]\[ \frac{G}{100} = \frac{D}{90} = \frac{2R}{\pi} \][/tex]

Where:
- [tex]\( G \)[/tex] is the angle in grades,
- [tex]\( D \)[/tex] is the angle in degrees,
- [tex]\( R \)[/tex] is the angle in radians.

To prove this, let's consider two relations and then combine them to establish the final equation.

### Step 1: Proving the Relation [tex]\(\frac{G}{100} = \frac{D}{90}\)[/tex]

1. By definition, the total measurement around a circle can be expressed in different units:
- A full circle is [tex]\(400\)[/tex] grades,
- A full circle is [tex]\(360\)[/tex] degrees.

2. Therefore, the proportion of grades to degrees for any angle would be:
[tex]\[ \frac{G \text{ (grades)}}{400} = \frac{D \text{ (degrees)}}{360} \][/tex]

3. Simplifying this equation:
[tex]\[ \frac{G}{400} = \frac{D}{360} \][/tex]

4. Multiplying both sides of the equation by [tex]\( \frac{9}{10} \)[/tex]:
[tex]\[ \frac{G}{400} \cdot \frac{9}{10} = \frac{D}{360} \cdot \frac{9}{10} \][/tex]
[tex]\[ \frac{G}{400} \cdot \frac{9}{10} = \frac{D}{40} \cdot \frac{1}{10} \][/tex]
[tex]\[ \frac{G}{100} = \frac{D}{90} \][/tex]

Thus, we have proved that:
[tex]\[ \frac{G}{100} = \frac{D}{90} \][/tex]

### Step 2: Proving the Relation [tex]\(\frac{D}{90} = \frac{2R}{\pi}\)[/tex]

1. By definition, the total measurement around a circle can also be expressed in radians:
- A full circle is [tex]\(2\pi\)[/tex] radians,
- A full circle is [tex]\(360\)[/tex] degrees.

2. Therefore, the proportion of degrees to radians for any angle would be:
[tex]\[ \frac{D \text{ (degrees)}}{360} = \frac{R \text{ (radians)}}{2\pi} \][/tex]

3. Simplifying this equation:
[tex]\[ \frac{D}{360} = \frac{R}{2\pi} \][/tex]

4. Multiplying both sides of the equation by [tex]\(4\)[/tex]:
[tex]\[ 4 \cdot \frac{D}{360} = 4 \cdot \frac{R}{2\pi} \][/tex]
[tex]\[ \frac{D}{90} = \frac{2R}{\pi} \][/tex]

Thus, we have proved that:
[tex]\[ \frac{D}{90} = \frac{2R}{\pi} \][/tex]

### Step 3: Combining Both Relations

Since we have established the following equalities:
[tex]\[ \frac{G}{100} = \frac{D}{90} \][/tex]
[tex]\[ \frac{D}{90} = \frac{2R}{\pi} \][/tex]

We can combine them to get:
[tex]\[ \frac{G}{100} = \frac{D}{90} = \frac{2R}{\pi} \][/tex]

Therefore, we have successfully proven that:
[tex]\[ \frac{G}{100} = \frac{D}{90} = \frac{2R}{\pi} \][/tex]