Question

If x : 3 = 12 : x, calculate the positive value of x

Answer 1

x : 3 = 12 : x

x/ 3 = 12/ x

With the help of cross multiplication,  

x * x = 12 * 3

x ^ 2 = 2 * 2 * 3 * 3

square rooting on both side

square root of x^2 = square root of [2 * 2 * 3 * 3]

x = 2 * 3

x = 6

Answer 2

Answer:

a:3=12:a

a/3 = 12/a

a^2=36

a=√36

a=6