CBSE Class 10 Answered
1)Let us assume that is a rational; where a and b are co prime,
so,b =a
So, squaring both sides, we get
5b2 = a2
Therefore a2 is dividable by 5 and also a is divisible by 5.
Now we can write a=5c for some integer c.
Substituting this value of for a, in (1) we get
5 i.e
This means that is divisible by 5 and also b is divisible by 5. Therefore a and b have 5 as their common factor, but this contradicts the fact that a and b are co prime. The contradiction arises because of our wrong assumption that is a rational.
So, we conclude that is an irrational.
2)Suppose is not an irrational number, then it must be a rational number.
So let =q where q is a rational number.
2+5+2
So here we have an equation with its left side is a rational number(as the set of rational numbers is closed under subtraction and division i.e the subtraction and division of two rational numbers is always a rational number)and so its right side must also be a rational number.
is a rational number
Which is a contradiction. So our basic assumption must be wrong.
=q where q is a rational number,is wrong
is an irrational number.
Hence proved.
similarly we can prove the other parts.