# Ex 12.4 Q2 Algebraic Expressions Solution - NCERT Maths Class 7

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## Question

Use the given algebraic expression to complete the table of number patterns.

 S. No. Expression Terms 1st 2nd 3rd 4th 5th ... 10th … 100th … (i) $$2n – 1$$ $$1$$ $$3$$ $$5$$ $$7$$ $$9$$ - $$19$$ - - - (ii) $$3n+2$$ $$5$$ $$8$$ $$11$$ $$14$$ - - - - - - (iii) $$4n + 1$$ $$5$$ $$9$$ $$13$$ $$17$$ - - - - - - (iv) $$7n + 20$$ $$27$$ $$34$$ $$41$$ $$48$$ - - - - - - (v) $$n^2 +1$$ $$2$$ $$5$$ $$10$$ $$17$$ - - - - $$10,001$$ -

Video Solution
Algebraic Expressions
Ex 12.4 | Question 2

## Text Solution

What is known?

Different algebraic expressions and the terms.

What is unknown?

Some terms of the given algebraic expression.

Reasoning:

This question is very simple put the value of n in the given algebraic expression and you can easily find out the unknown terms.

Steps:

Putting value of $$n = 5, 10$$ and $$100$$

(i) $$2n – 1$$

\begin{align}2 \times 100 - 1 & = 200 - 1\\& = 199\end{align}

(ii) $$3n+2$$

\begin{align}3 \times 5 + 2 & = 15 + 2\\ & = 17\\\ 3 \times 10 + 2&=30+ 2\\ &= 32 \\ 3 \times 100 + 2 & = 300 + 2\\& = 302\\\end{align}

(iii) $$4n+1$$

\begin{align}4 \times 5 + 1& = 20 + 1\\&= 21\\ 4 \times 10 + 1&= 40 + 1\\ & = 41\\4 \times 100 + 1&= 400 + 1\\ & = 401\end{align}

(iv) $$7n+2$$

\begin{align}7 \times 5 + 20 & = 35 + 20\\&= 55\\7 \times 10 + 20 & = 70 + 20\\&= 90\\7 \times 100 + 20 & = 700 + 20\\&= 720\end{align}

(v) $$n^2+1$$

\begin{align}5 \times 5 + 1 & = 25 + 1\\& = 26\\10 \times 10 + 1 & = 100 + 1\\& = 101\\100 \times 100 + 1 & = 10000 + 1\\& = 10001\end{align}

Complete table is:

 S.No. Expression Terms 1st 2nd 3rd 4th 5th ... 10th … 100th … (i) $$2n – 1$$ $$1$$ $$3$$ $$5$$ $$7$$ $$9$$ - $$19$$ - $$199$$ - (ii) $$3n + 2$$ $$5$$ $$8$$ $$11$$ $$14$$ $$17$$ - $$32$$ - $$302$$ - (iii) $$4n + 1$$ $$5$$ $$9$$ $$13$$ $$17$$ $$21$$ - $$41$$ - $$401$$ - (iv) $$7n + 20$$ $$27$$ $$34$$ $$41$$ $$48$$ $$55$$ - $$90$$ - $$720$$ - (v) $$n^2 + 1$$ $$2$$ $$5$$ $$10$$ $$17$$ $$26$$ - $$101$$ - $$10,001$$ -

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