arithmetic

Question

A number whose square is 4 less than twice the square of 10

 

Answer 1

Let x = the unknown number.  We want a number (x) whose square (x²) is 4 less (- 4) than twice the square of 10 (2*10²):

 

x² = 2*10² - 4

x² = 2*100 - 4

x² - 200 - 4

x² = 196

x = ±√196

x = ±14

Answer 2

Let the number be n

Then 

n² =2(10)² -4

n² = 200-4=196

n=14 or -14