when you square five times a number you get three more than the number

Question

writting equations

Answer 1

Let x be the number.

 

So, the square of 5 times the number is (5x)² which equals 25 x^2.

 

But that is equal to three more than the number, or x + 3.

 

so 25x² = x + 3.

 

25x² - x - 3 = 0.

 

Since you referred to this problem as "writing equations," that may be all you need.  Do you need to solve the equation too?  If so, you would use the quadratic formula.