Question

8 times of a number is added to its square give a result -15. Then find the number by using its quadratic equation.
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Answer 1

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8 times of a number is added to its square give a result -15. Then find the number by using its quadratic equations

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Let us consider the given number = x

Then it's square = x²

8 times of it = 8x

Now adding the above two x² + 8x

result is = -15

⛬ x² + 8x = -15

➪ x² + 8x + 15 = 0

➪ x² + 5x + 3x + 15 = 0

➪ x(x + 3) + 3(x + 5) = 0

➪ (x + 3) (x + 5) = 0

⛬ x + 3 = 0 or x + 5 = 0

Then x = -3 or -5

Answer 2

Answer:

ANSWER

Let the number be x

Given 

x is added to twice its x2 gives 21

2x2+x=21

⟹2x2+x−21=0

⟹2x2+7x−6x−21=0

⟹x(2x+7)−3(2x+7)=0

⟹(x−3)(2x+7)=0

⟹x=3,−27

The number is 3,−27

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