If (28-x) is the mean proportional of (23-x) and (19-x) then find the value of x.

If the mean of 20, 18 ,13 ,12, x and 10 is 15, then find the value of x.

If 10 is the geometric mean of 25 and x,then find the value of x.

(x-4) is geometric mean of (x-5) and (x-2) find the value of x

For x=0, find the value of x^2 -5x+5

If (x+3):(x+11)=(x-2):(x+1) , then find the value of x.

If (x+5) : (x+7) = (x-1): (x+2) , find the value of x.

Solve the following questions : If the value of the polynomial x^3 + 3x + a for x = 2 is 9 , then find the value of a .