Question

if a number is added to twice its square ,the result is 21 . find the number.

Answer 1

3 is the right number

Answer 2

Answer:

The answer is : 3 , -7/2

Step-by-step explanation:

Let the number be x

According to the question ,

2x^2 + x = 21

2x^2 + x -21 = 0

2x^2 - 6x + 7x -21 = 0 (by splitting middle term)

2x(x-3) 7(x-3) = 0

(x-3)(2x+7) = 0

Case (i)

x-3 = 0

x = 3

Case (ii)

2x + 7 = 0

2x = -7

x = -7/2

Answer : x = 3 , -7/2

The number is 3 , -7/2