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Ffocws dysgu

Dysga adnabod rhifau cysefin fel rhifau sydd â dim ond dau ffactor.

Mae'r wers hon yn cynnwys:

• un fideo
• un gweithgaredd

Learning focus

Learn to identify prime numbers as numbers having only two factors.

This lesson includes:

• one video
• one activity

Fideo / Video

Nodiadau i rieni

Ar ôl gwylio'r fideo, bydd disgyblion yn deall y canlynol.

• Mae rhif cysefin dim ond yn gallu cael ei rhannu gydag 1 a’r rhif ei hun.
• Mae 3 yn rhif cysefin gan nad yw e’n bosibl iddo gael ei rannu gydag unrhywbeth heblaw 1 a 3. Hynny yw, dim ond 1 a 3 sy’n mynd i mewn i 3 (mae 1 a 3 yn ffactorau o 3).
• Nid yw 4 yn rhif cysefin oherwydd rydym yn gallu ei rannu gydag 1, 2 a 4. Hynny yw, mae ganddo fwy na phâr o ffactorau.
• Mae 5 yn rhif cysefin gan taw dim ond 1 a 5 sy’n mynd i mewn iddo. Dim ond dau ffactor sydd gan 5.
• Nid yw 1 yn rhif cysefin gan taw dim ond un ffactor sydd ganddo.

Notes for parents

After watching the video, students will understand the following.

• A prime number can only be divided by 1 and the number itself.
• 3 is a prime number as it’s not possible to divide this number by anything other than 1 and 3. In other words, only 1 and 3 go into 3 (1 and 3 are both factors of 3).
• 4 is not a prime number as you can divide this number by 1, 2 and 4. Therefore, it has more than a pair of factors.
• 5 is a prime number as 1 and 5 are the only numbers that can go into it. Therefore, it only has a pair of factors.
• 1 is not a prime number as it only has a single factor.

Rhifau cysefin

Mae rhifau cysefin yn rhifau arbennig sydd ddim ond yn gallu cael eu rhannu gyda’u hunain ac 1.

Mae 19 yn rhif cysefin. Dim ond 1 ac 19 sy’n gallu rhannu i mewn iddo.

Dydy 9 ddim yn rhif cysefin. Mae’n gallu cael ei rannu gyda 3 yn ogystal ag 1 a 9.

Dyma’r rhifau cysefin o dan 20: 2, 3, 5, 7, 11, 13, 17, 19.

Primary numbers are special numbers that can only be divided by themselves.

The number 19 is a primary number. Only 1 and 19 can be divided into it.

The number 9 is not a primary number. It can be divided by 3 as well as 1 and 9.

Here are the primary numbers under 20: 2, 3, 5, 7, 11, 13, 17, 19.

Gweithgaredd / Activity

Dewisa’r rhifau cysefin.

Select the prime numbers.