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Q1(iv):
Fill in the blanks in the following table, given that $a$ is the first term, $d$ the common difference and $a_n$ the $n$th term of the AP: (iv) $a=–18.9, d=2.5, n=..., a_n=3.6$

Solution :

Given:

The first term of the Arithmetic Progression (AP), $a = -18.9$

The common difference of the AP, $d = 2.5$

The $n^{th}$ term of the AP, $a_n = 3.6$

To find:

The number of terms, $n$.

Formula:

The $n^{th}$ term of an Arithmetic Progression is given by the formula:

$a_n = a + (n - 1)d$

Step 1: Substitution of given values into the formula

Substitute $a = -18.9$, $d = 2.5$, and $a_n = 3.6$ into the formula $a_n = a + (n - 1)d$:

$3.6 = -18.9 + (n - 1)(2.5)$

Step 2: Isolating the term containing $n$

Add $18.9$ to both sides of the equation to isolate the term with $(n-1)$:

$3.6 + 18.9 = (n - 1)(2.5)$

$22.5 = (n - 1)(2.5)$

Step 3: Solving for $(n - 1)$

Divide both sides of the equation by $2.5$:

$\frac{22.5}{2.5} = n - 1$

[Since $\frac{22.5}{2.5} = \frac{225}{25} = 9$]

$9 = n - 1$

Step 4: Solving for $n$

Add $1$ to both sides of the equation:

$n = 9 + 1$

$n = 10$

Conclusion:

By substituting the given values into the standard formula for the $n^{th}$ term of an AP and performing algebraic simplification, we determine that the number of terms $n$ is $10$.

Final Answer: n = 10


More Questions from Class 10 Mathematics Arithmetic Progression EXERCISE 5.2


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