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5. It is given that [tex]y[/tex] is directly proportional to [tex]x^2[/tex]. It is known that [tex]y = 10[/tex] when [tex]x = 2[/tex]. Find the value of [tex]y[/tex] when [tex]x[/tex] is doubled.



Answer :

To solve this problem, we'll go step by step.

1. Understand the relationship:
- The problem states that [tex]\( y \)[/tex] is directly proportional to [tex]\( x^2 \)[/tex]. Mathematically, this can be written as:
[tex]\[ y = k \cdot x^2 \][/tex]
where [tex]\( k \)[/tex] is the constant of proportionality.

2. Find the constant of proportionality [tex]\( k \)[/tex]:
- We're given that [tex]\( y = 10 \)[/tex] when [tex]\( x = 2 \)[/tex]. Substituting these values into the equation, we get:
[tex]\[ 10 = k \cdot 2^2 \][/tex]
- Simplify the equation to solve for [tex]\( k \)[/tex]:
[tex]\[ 10 = k \cdot 4 \][/tex]
[tex]\[ k = \frac{10}{4} \][/tex]
[tex]\[ k = 2.5 \][/tex]

3. Double the value of [tex]\( x \)[/tex]:
- We need to find the value of [tex]\( y \)[/tex] when [tex]\( x \)[/tex] is doubled. If [tex]\( x \)[/tex] is initially 2, then doubling it gives:
[tex]\[ x_{\text{new}} = 2 \times 2 = 4 \][/tex]

4. Calculate the new value of [tex]\( y \)[/tex]:
- Substitute [tex]\( x_{\text{new}} = 4 \)[/tex] back into the proportionality equation:
[tex]\[ y_{\text{new}} = k \cdot x_{\text{new}}^2 \][/tex]
- Using [tex]\( k = 2.5 \)[/tex] and [tex]\( x_{\text{new}} = 4 \)[/tex]:
[tex]\[ y_{\text{new}} = 2.5 \cdot 4^2 \][/tex]
[tex]\[ y_{\text{new}} = 2.5 \cdot 16 \][/tex]
[tex]\[ y_{\text{new}} = 40 \][/tex]

Hence, when the value of [tex]\( x \)[/tex] is doubled, the value of [tex]\( y \)[/tex] becomes 40.

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