CBSE Class 10 Answered
prove ?5 is irrational number
Asked by appusingh0840 | 29 Oct, 2023, 13:14: PM
Let √5 is a rational number.
Then we can write , √5 = p/q
where p and q are integers, q ≠ 0 and p and q are co-prime
( i..e. p and q do not have any common factor othr than 1 )
![begin mathsize 14px style square root of 5 space equals space p over q end style](https://images.topperlearning.com/topper/tinymce/cache/34ef1a3d582ae2da40b773c81963de51.png)
By squaring both sides we get ,
.......................(1)
![begin mathsize 14px style p squared over 5 equals space q squared end style](https://images.topperlearning.com/topper/tinymce/cache/f9a59394100b4746b0c7125f0b909716.png)
From above expression , we get 5 is factor of p .
hence we write , p = 5 c and p2 = 25 c2
Hence eqn.(1) becomes
![begin mathsize 14px style fraction numerator 25 space c squared over denominator 5 end fraction space equals space q squared end style](https://images.topperlearning.com/topper/tinymce/cache/574d2782d77fbd970545c1cf3732b95c.png)
![begin mathsize 14px style q squared over 5 space equals space c squared end style](https://images.topperlearning.com/topper/tinymce/cache/c8d30ca05113cefde4b599938b4cb0ae.png)
Hence q is divisible by 5 , or 5 is a factor of q .
Hence we get 5 is afctor of p and aloso factor of q .
But we have started with the assumption p and q are co-prime .
Hence √5 ≠ p/q if p and q are integers
Hence √5 is not a rational number and it is irrational number .
Answered by Thiyagarajan K | 29 Oct, 2023, 16:18: PM
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