# Ex.14.3 Q13 Factorization - NCERT Maths Class 8

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## Question

Find and correct the errors in the following mathematical statement.

Substituting $$x = - 3$$ in

(a)\begin{align}\quad{x^2} + 5x + 4\end{align} gives

\begin{align}&={{( - 3)}^2} + 5( - 3) + 4 \\&= 9 + 2 + 4 \\&= 15\end{align}

(b)\begin{align}\quad{x^2} - 5x + 4\end{align} gives

\begin{align}&={( - 3)}^2 - 5( - 3) + 4 \\&= 9 - 15 + 4 \\&= - 2\end{align}

(c)\begin{align}\quad{x^2} + 5x\end{align} gives

\begin{align}&={{( - 3)}^2} + 5( - 3)\\&= - 9 - 15 \\&= - 24\end{align}

## Text Solution

What is known?

Incorrect mathematical statement.

What is unknown?

Correct mathematical statement.

Reasoning:

Put value of $$x$$ in $$L.H.S$$ and find correct solution.

Steps:

(a) For $$x = -\, 3$$

\begin{align}L.H.S &= {x^2} + 5x + 4 \\&= {( - 3)^2} + 5( - 3) + 4\\&= 9 - 15 + 4\\& = 13 - 15\\& = - 2\\L.H.S &\ne R.H.S\\\end{align}

The correct statement is $${x^2} + 5x + 4=- 2$$

(b) For $$x = -\, 3$$

\begin{align}{x^2} - 5x + 4 &= {( - 3)^2} - 5( - 3) + 4\\& = 9 + 15 + 4\\&= 28\\\end{align}

The correct statement is$${x^2} - 5x + 4 = 28$$

(c) For $$x = - 3$$

\begin{align}{x^2} + 5x & = {( - 3)^2} + 5( - 3)\\& = 9 - 15\\& = - 6\end{align}

The correct statement is $${x^2} + 5x = - 6$$

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