Ex.12.3 Q1 Algebraic Expressions Solution - NCERT Maths Class 7

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Question

If \(m = 2\), find the value of:

(i)  \(m = 2\)

(ii) \(3m - 5\)

(iii) \({\rm{ }}9{\rm{ }}-{\rm{ }}5m\)

(iv) \(3{m^2} - 2m - 7\)

(v) \(\begin{align} \frac{{5m}}{2} - 4\end{align} \)

Text Solution

What is Known?

Value of \(m\).

What is unknown?

Value of the given expressions.

Reasoning:

This is based on concept of putting given value of variable and then performing the arithmetic operation as given in the question.

Steps:

Value of \(m\) is given as \( 2\).

 (i)  \(m = 2\)

\[\begin{align}& {\rm{ = 2}} - {\rm{2}}\\{\rm{ Ans }} &{\rm{ = }}\,{\rm{0 }}\end{align}\]

(ii) \(3m - 5\)

\[\begin{align}& = 3 \times 2 - \left( 5 \right)\\& = 6 - 5\\{\rm{ Ans }} &= 1\end{align}\]

(iii) \({\rm{ }}9{\rm{ }}-{\rm{ }}5m\)

\[\begin{align}& = 9 - \left( {5 \times 2} \right)\\& = 9 - 10\\{\rm{ Ans }} &= - 1\end{align}\]

(iv) \(3{m^2} - 2m - 7\)

\[\begin{align}& = 3{{\left( 2 \right)}^2} - \left( {2 \times 2} \right) - 7\\& = 3 \times 2 \times 2 - \left( 4 \right) - 7\\& = 12 - 4 - 7\\{\rm{ Ans }} & = 1\end{align}\]

(v) \(\begin{align} \frac{{5m}}{2} - 4\end{align} \)

\[\begin{align}& = \frac{{5 \times 2}}{2} - 4\\& = \frac{{10}}{2} - 4\\& = 5 - 4\\{\rm{ Ans }} & = 1\end{align}\]