Question

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

Answer 1

Let us consider the given number = x Then its 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 + 5) + 3(x + 5) = 0 

⇒ (x + 3) (x + 5) = 0 

∴ x + 3 = 0 or x + 5 = 0 

Then x = – 3 or – 5