Show root 5 is irrational number
Answers
Let us assume that √5 is a rational number
{ for now }
Sp it t can be expressed in the form p/q where p,q are co-prime integers and q≠0
⇒√5=p/q
On squaring both the sides we get,
⇒5=p²/q²
⇒5q²=p² —————–(i)
p²/5= q²
So 5 divides p
p is a multiple of 5
⇒p=5m
⇒p²=25m² ————-(ii)
From equations (i) and (ii), we get,
5q²=25m²
⇒q²=5m²
⇒q² is a multiple of 5
⇒q is a multiple of 5
Hence, p,q have a common factor 5. This contradicts our assumption that they are co-primes. Therefore, p/q is not a rational number
√5 is an irrational number
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ʟᴇᴛ ᴜs ᴀssᴜᴍᴇ ᴛʜᴀᴛ √5 ɪs ᴀ ʀᴀᴛɪᴏɴᴀʟ ɴᴜᴍʙᴇʀ.
ᴡᴇ ᴋɴᴏᴡ ᴛʜᴀᴛ ᴛʜᴇ ʀᴀᴛɪᴏɴᴀʟ ɴᴜᴍʙᴇʀs ᴀʀᴇ ɪɴ ᴛʜᴇ ғᴏʀᴍ ᴏғ ᴘ/ǫ ғᴏʀᴍ ᴡʜᴇʀᴇ ᴘ,ǫ ᴀʀᴇ ɪɴᴛᴇᴢᴇʀs.
sᴏ, √5 = ᴘ/ǫ
ᴘ = √5ǫ
ᴡᴇ ᴋɴᴏᴡ ᴛʜᴀᴛ 'ᴘ' ɪs ᴀ ʀᴀᴛɪᴏɴᴀʟ ɴᴜᴍʙᴇʀ. sᴏ √5 ǫ ᴍᴜsᴛ ʙᴇ ʀᴀᴛɪᴏɴᴀʟ sɪɴᴄᴇ ɪᴛ ᴇǫᴜᴀʟs ᴛᴏ ᴘ
ʙᴜᴛ ɪᴛ ᴅᴏᴇsɴᴛ ᴏᴄᴄᴜʀs ᴡɪᴛʜ √5 sɪɴᴄᴇ ɪᴛs ɴᴏᴛ ᴀɴ ɪɴᴛᴇᴢᴇʀ
ᴛʜᴇʀᴇғᴏʀᴇ, ᴘ =/= √5ǫ
ᴛʜɪs ᴄᴏɴᴛʀᴀᴅɪᴄᴛs ᴛʜᴇ ғᴀᴄᴛ ᴛʜᴀᴛ √5 ɪs ᴀɴ ɪʀʀᴀᴛɪᴏɴᴀʟ ɴᴜᴍʙᴇʀ
ʜᴇɴᴄᴇ ᴏᴜʀ ᴀssᴜᴍᴘᴛɪᴏɴ ɪs ᴡʀᴏɴɢ ᴀɴᴅ √5 ɪs ᴀɴ ɪʀʀᴀᴛɪᴏɴᴀʟ ɴᴜᴍʙᴇʀ.
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