Question

Twenty times a position integer its square by 156. What is integer?

Answer 1

Answer:

the unknown number x, the following equation is the result:

20x = x^2 -96

so x^2 - 20x - 96 = 0.

Using the quadratic formula:

(20+/-root400–4*1*-96)/2

so (20+/-root784)/2

This becomes (20+/- 2*root196)/2

then (20+/-4*root49)/2

As root49=7, you are left with (20+/-28)/2

which gives the answers of 24 and -4.

You want a positive integer so discard the -4 and take 24 as the answer.

Sorry for showing the intermediate stages but I was working without a calculator.