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Q4(xii):
Which of the following are APs ? If they form an AP, find the common difference $d$ and write three more terms. (xii) $\sqrt{2}, \sqrt{8}, \sqrt{18}, \sqrt{32}, . . .$

Solution :

Given: A sequence of numbers: $\sqrt{2}, \sqrt{8}, \sqrt{18}, \sqrt{32}, \dots$

To Find: Determine if the sequence forms an Arithmetic Progression (AP). If it does, find the common difference $d$ and the next three terms.

Step 1: Simplify the given terms
To analyze the sequence, we first simplify each radical term by extracting perfect square factors:
Term 1 ($a_1$) = $\sqrt{2} = 1\sqrt{2}$
Term 2 ($a_2$) = $\sqrt{8} = \sqrt{4 \times 2} = 2\sqrt{2}$
Term 3 ($a_3$) = $\sqrt{18} = \sqrt{9 \times 2} = 3\sqrt{2}$
Term 4 ($a_4$) = $\sqrt{32} = \sqrt{16 \times 2} = 4\sqrt{2}$
The sequence is: $\sqrt{2}, 2\sqrt{2}, 3\sqrt{2}, 4\sqrt{2}, \dots$

Step 2: Verify if the sequence is an AP
A sequence is an AP if the difference between consecutive terms is constant. This constant is called the common difference ($d$).
Calculate the differences between consecutive terms:
$d_1 = a_2 - a_1 = 2\sqrt{2} - 1\sqrt{2} = (2-1)\sqrt{2} = \sqrt{2}$
$d_2 = a_3 - a_2 = 3\sqrt{2} - 2\sqrt{2} = (3-2)\sqrt{2} = \sqrt{2}$
$d_3 = a_4 - a_3 = 4\sqrt{2} - 3\sqrt{2} = (4-3)\sqrt{2} = \sqrt{2}$

[Since $d_1 = d_2 = d_3 = \sqrt{2}$, the difference between consecutive terms is constant.]
Therefore, the given sequence is an Arithmetic Progression with common difference $d = \sqrt{2}$.

Step 3: Find the next three terms
The sequence currently has four terms. We need to find the 5th, 6th, and 7th terms using the formula $a_n = a_{n-1} + d$.
Term 5 ($a_5$) = $a_4 + d = 4\sqrt{2} + \sqrt{2} = 5\sqrt{2} = \sqrt{25 \times 2} = \sqrt{50}$
Term 6 ($a_6$) = $a_5 + d = 5\sqrt{2} + \sqrt{2} = 6\sqrt{2} = \sqrt{36 \times 2} = \sqrt{72}$
Term 7 ($a_7$) = $a_6 + d = 6\sqrt{2} + \sqrt{2} = 7\sqrt{2} = \sqrt{49 \times 2} = \sqrt{98}$

Final Answer: The sequence forms an AP with common difference $d = \sqrt{2}$. The next three terms are $\sqrt{50}, \sqrt{72}, \text{ and } \sqrt{98}$.


More Questions from Class 10 Mathematics Arithmetic Progression EXERCISE 5.1


CBSE Solutions for Class 10 Mathematics Arithmetic Progression


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