# Canfod yr nfed term

Weithiau, yn hytrach na chanfod y rhif nesaf mewn dilyniant llinol, efallai fod arnot angen canfod y $${41}^{fed}$$ rhif, neu’r $${110}^{fed}$$ rhif.

Mae ysgrifennu $${41}$$ neu $${110}$$ o rifau’n cymryd amser, felly gelli di ddefnyddio rheol gyffredinol.

I ganfod gwerth unrhyw derm mewn dilyniant, defnyddia reol yr $${n}^{fed}$$ term.

Question

Beth ydy $${n}^{fed}$$ term y dilyniant hwn?

$${1}^{af}$$ = $${5}$$ $$({5}\times{1})$$; $${2}^{ail}$$ = $${10}$$ $$({5}\times{2})$$; $${3}^{ydd}$$ = $${15}$$ $$({5}\times{3})$$

Felly yr $${n}^{fed}$$ term ydy $${5}\times{n}$$ neu $${5n}$$

Er enghraifft, i ganfod y $${10}^{fed}$$ term, cyfrifa $${5}\times{10} = {50}$$. I ganfod y $${7}^{fed}$$ term, cyfrifa $${5}\times{7} = {35}$$

Felly y $${41}^{fed}$$ term ydy $${5}\times{41} = {205}$$ a’r $${110}^{fed}$$ term ydy $${5}\times{110} = {550}$$

Question

Beth ydy $${n}^{fed}$$ term a $${10}^{fed}$$ term y dilyniant hwn: $${2},~{4},~{6}, ...$$ ?

$${n}^{fed}$$ term $$= {2n}$$

$${10}^{fed}$$ term $$= {20}$$. I gyfrifo hyn, $${n} = {10}$$, felly $${2n} = {2}\times{10} = {20}$$