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Siâp a Gofod / Shape and Space

Siâp a Gofod / Shape and Space. ONGLAU ALLANOL / EXTERNAL ANGLES. ONGLAU ALLANOL / EXTERNAL ANGLES. Yr ongl allanol yw’r ongl sydd raid i’r saeth ei droi pan yn newid cyfeiriad o AB i BC. The external angle is the angle that the arrow needs to turn when changing direction from AB to BC.

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Siâp a Gofod / Shape and Space

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  1. Siâp a Gofod / Shape and Space ONGLAU ALLANOL / EXTERNAL ANGLES

  2. ONGLAU ALLANOL / EXTERNAL ANGLES • Yr ongl allanol yw’r ongl sydd raid i’r saeth • ei droi pan yn newid cyfeiriad o AB i BC. • The external angle is the angle that the • arrow needs to turn when changing • direction from AB to BC. C B A

  3. SGWÂR / SQUARE Mae’r pedair ongl yn creu 360° The four angles create 360° 360 ÷ 4 = 90° Mae un ongl allanol yn 90° One external angle is 90°

  4. PENTAGON RHEOLAIDDREGULAR PENTAGON Mae’r pump ongl yn creu 360° The five angles create 360° 360 ÷ 5 = 72° Mae un ongl allanol yn 72° One external angle is 72°

  5. HECSAGON RHEOLAIDDREGULAR HEXAGON Mae’r chwe ongl yn creu 360° The six angles create 360° 360 ÷ 6 = 60° Mae un ongl allanol yn 60° One external angle is 60°

  6. YMARFERION / EXERCISES • 1. Cyfrifwch ongl allanol heptagon rheolaidd (7 ochr). • 1. Calculate the external angle of a regular heptagon (7 sides). • 2. Cyfrifwch ongl allanol octagon rheolaidd (8 ochr). • 2. Calculate the external angle of a regular octagon (8 sides). • 3. Cyfrifwch ongl allanol nonagon rheolaidd (9 ochr). • 3. Calculate the external angle of a regular nonagon (9 sides). • 4. Cyfrifwch ongl allanol decagon rheolaidd (10 ochr). • 4. Calculate the external angle of a regular decagon (10 sides). • 5. Cyfrifwch ongl allanol hendecagon rheolaidd (11 ochr). • 5. Calculate the external angle of a regular hendecagon (11 sides). • 6. Cyfrifwch ongl allanol dodecagon rheolaidd (12 ochr). • 6. Calculate the external angle of a regular dodecagon (12 sides). • Beth mae’r ongl allanol yn nesau ato wrth i nifer yr ochrau gynyddu? • What does the external angle tend to when the number of sides increase?

  7. POLYGON AFREOLAIDD IRREGULAR POLYGON • Mae cyfanswm onglau allanol polygon bob amser yn adio i 360° • The sum of external angles of a polygon always adds to 360° 73° 73° 65° 65° 59° 22° + 219° 59° 360° A _ 219° 22° 141° A = 141°

  8. POLYGON AFREOLAIDD IRREGULAR POLYGON • Mae cyfanswm onglau allanol polygon bob amser yn adio i 360° • The sum of external angles of a polygon always adds to 360° 88° 45° 45° 38° 88° 38° 43° 25° + 239° 43° 360° _ 239° 25° B 121° B = 121°

  9. YMARFERION / EXERCISES • Cyfrifwch yr onglau sydd wedi eu nodi â llythyren • Calculate the angles marked with letters 80° 66° 75° 100° 98° 91° B A 95° C 90° 85° 57° 25° 33°

  10. ALLANOL + MEWNOL = 180°EXTERNAL + INTERNAL = 180° • Wrth adio ongl allanol at ongl fewnol • mae’r cyfanswm bob amser yn 180° • Adding the external and • internal angles together • always gives a total of 180° • Mae hyn yn wir ar gyfer • polygon rheolaidd ac • afreolaidd • This is true for regular • and irregular polygons

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