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Q1(iii):
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: (iii) $a=..., d=–3, n=18, a_n=–5$

Solution :

Given:

The common difference of the Arithmetic Progression (AP), $d = -3$.

The number of terms in the AP, $n = 18$.

The $n$th term of the AP, $a_n = -5$.

To find:

The first term of the AP, denoted by $a$.


Step 1: Stating the General Formula for an Arithmetic Progression

The $n$th term of an Arithmetic Progression is given by the standard formula:

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

[Where $a_n$ is the $n$th term, $a$ is the first term, $n$ is the position of the term, and $d$ is the common difference.]


Step 2: Substituting the Given Values into the Formula

Substitute $a_n = -5$, $n = 18$, and $d = -3$ into the equation:

$-5 = a + (18 - 1)(-3)$


Step 3: Simplifying the Expression

First, perform the subtraction inside the parentheses:

$-5 = a + (17)(-3)$

[Since $18 - 1 = 17$]


Next, perform the multiplication:

$-5 = a - 51$

[Since $17 \times -3 = -51$]


Step 4: Solving for $a$

To isolate $a$, add $51$ to both sides of the equation:

$-5 + 51 = a$

$a = 46$


Final Answer: The first term of the Arithmetic Progression is 46.


More Questions from Class 10 Mathematics Arithmetic Progression EXERCISE 5.2


CBSE Solutions for Class 10 Mathematics Arithmetic Progression


Chapters in CBSE - Class 10 Mathematics


Other Subjects in CBSE - Class 10

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