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Question 9
If the edge of a cube is increased by 4 cm, the volume will increase by 988$$cm^3$$. Then the original length of each edge of the cube is
Solution
Let x be the original size of the cube.
If the edge of a cube is increased by 4 cm, the volume will increase by 988$$cm^3$$.
According to question,
$$(x+4)^3-x^3=988$$
$$x^3+12x^2+48x+64-x^3 = 988$$
$$12x^2+48x=988-64$$
$$12x^2+48x-924=0$$
$$x^2+4x-77=0$$
$$x=-11,7$$
x = 7 cm
Option A is correct.
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