Answer: x = 8
Step-by-step explanation: Let 'x' be the number we are looking for.
As per the question, equation will be : x^2 - 40 = 3x
x^2 - 3x - 40 = 0
Factor the equation. Or quadratic equation formula can also be used.
Factoring -
x^2 - 3x - 40 = 0
x^2 - 8x + 5x - 40 = 0
x(x-8) + 5( x-8) = 0
(x+5) ( x-8) = 0
x+5=0 , x-8 =0
x = -5 , x = 8
As we need to find the positive solution, x = 8 is the answer.
VERIFICATION -
= x^2 - 40
= ( 8 )^2 - 40
= 64 - 40
= 24
And 3 times 8 is also 24.
Therefore, if we subtract 40 from the square of 8, the result will be 3 times the number (which is 8).