Question

The square of a number when decreased by 15 is equal to twice the original number. Which of the following are true about the numbers?

• A. 8, 7
• B. 9, 6
• C. 2, -7
• D. 5, -3

Answer 1

Answer: (C), (D)

The correct options are
C

2, -7

D

5, -3

Let the number be $x$.

Given, $x^2-15=2x$

$\Rightarrow$ $x^2-2x-15=0$

$\Rightarrow$ $x^2-5x+3x-15=0$

$\Rightarrow$ $x(x-5)+3(x-5)=0$

$(x-5)(x+3)=0$

$\Rightarrow$ $x=5andx=-3$