# Ex.12.3 Q5 Algebraic Expressions Solution - NCERT Maths Class 7

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## Question

When $$a = 0$$, $$b = \,– 1$$, find the value of the given expressions:

(i) $$2a+\text{ }2b$$

(ii) $$2{{a}^{2}}+{{b}^{2}}+\text{ }1$$

(iii) $$2{{a}^{2}}b+\text{ }2a{{b}^{2}}+ab$$

(iv) $${{a}^{2}}+ab+\text{ }2$$

## Text Solution

What is Known?

Value of $$a$$ and $$b$$

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 $$a$$ is given as $$0$$ and $$b$$ is $$–1$$

(i) $$2a+\text{ }2b$$

\begin{align}& = \left( {2 \times 0} \right) + \left( {2 \times - 1} \right)\\& = 0 + \left( { - 2} \right)\\{\rm{ Ans }} & = - 2\end{align}

(ii) $$2{{a}^{2}}+{{b}^{2}}+\text{ }1$$

\begin{align}& = \left( {2 \times {0^2}} \right) + {\left( { - 1} \right)^2} + 1\\ & = 0 + 1 + 1\\& = 2\end{align}

(iii) $$2{{a}^{2}}b+\text{ }2a{{b}^{2}}+ab$$

\begin{align} &= \left[ \begin{array}{l}\,\,2 \times 0 \times 0 \times - 1 + \\\left( {2 \times 0 \times - {1^2}} \right) + 0 \times - 1\end{array} \right]\\ &= 0 + 0 + 0\\{\rm{Ans}} &= 0\end{align}

(iv) $${{a}^{2}}+ab+\text{ }2$$

\begin{align}& = {0^2} + 0 \times - 1 + 2\\& = 0 + 0 + 2\\{\rm{ Ans }} & = 2\end{align}

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