Calculation:
Let's check each option one by one:
Option 1: (√2+√81)2
Step 1: Simplify the terms.
√81=2√21
Step 2: Substitute in the original expression:
(√2+2√21)2
Step 3: Apply the expansion formula (a+b)2=a2+2ab+b2
a=√2,b=2√21
⇒ 2 + 2 × √2 × 2√21 + (2√21)2 = 4 + 1 + 1/8 = 41/8
Result:
This expression is a rational number.
Option 2: 2 - √{5}
This is a subtraction of a rational number and an irrational number √{5}. The result will be irrational.
Option 3: (√2+√5)2
Step 1: Apply the expansion formula (a+b)2=a2+2ab+b2
a=√2,b=√5
Step 2: Simplify:
a2=2, b2=5, 2ab=2×√2×√5=2√10
The result will still involve irrational terms, so it is not a rational number.
Option 4: 2 + √{5}
This is a sum of a rational number and an irrational number √{5}. The result will be irrational.
∴ The correct answer is option 1.