Help I want to understand how to do this

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Step-by-step explanation:

The measure of an arc of a circle is the same as the measure of the central angle it subtends. That is, arc RS has the same measure as central angle RPS, which is marked as 100°.

Of course, the total of all central angles, hence all arcs, of a circle is 360°. A diameter of a circle cuts the circle in half, so each semicircle has a central angle measure and arc measure of 180°.

Any arc that is more than a semicircle is called a "major" arc. If it is less than a semicircle, it is a "minor" arc. Arcs RS and ST are minor arcs.

As always in geometry, the whole is the sum of the parts, so arcs RS and ST are supplementary. They total the measure of semicircle RST, which is 180°. Then ST = 180° -RS = 180° -100° = 80°.

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Additional comment

Usually, an arc identified only by its end points is a minor arc. If the major arc is intended, then it will either be described as "major arc RS" or a point on the major arc will be given, as "arc RTS". The measure of arc RTS is 280°.

i use my brain for prombles like this maybe you could try it

step-by-step explanation:

the value of x is 9 ⇒ answer b

step-by-step explanation:

* we can solve this problem using cosine and sine rule

- in δ abc

∵ ab = 36 , bc = 28 , ac = 16

- lets find the measure of angle b using the cosine rule

∵ cos b = [ab² + bc² - ac²]/2(ab)(bc)

∴ cos b = [36² + 28² - 16²]/2(36)(28)

∴ cos b = 19/21

∴ m∠b = cos^-1(19/21) ≅ 25°

- lets find the measure of angle a using the sine rule

∵ sina/bc = sinb/ac = sinc/ab

∴ sina/28 = sin25°/16 ⇒ by using cross multiplication

∴ sina = 28 × sin25°/16

∴ sina = 0.7396

∴ m∠a = sin^-1(0.7396) ≅ 48°

- from the figure m∠abd = m∠dbc

∵ m∠abc = 25°

∴ m∠abd = 25°/2 = 12.5°

- in δabd

∵ m∠a = 48° , m∠abd = 12.5°

∵ the sum of the measures of the interior angles of any δ is 180°

∴ m∠adb = 180° - (48° + 12.5°) = 119.5°

∵ ab = 36

∵ ad = x

- use the sine rule to find x

∵ sin∠adb/ab = sin∠abd/x

∴ sin119.5°/36 = sin12.5°/x ⇒ by using cross multiplication

∴ x = 36 × sin12.5°/sin119.5° = 8.95 ≅ 9

* the value of x is 9