Question 290686
The average of two numbers a and b is C,
{{{(a+b)/2}}} = c
a + b = 2c
:
and the product of a and b is D.
ab = d
:
What is then a^2 + b^2
:
We know (a+b)*(a+b) = a^2 + 2ab + b^2
then
2c * 2c = 4c^2 = a^2 + 2ab + b^2 
we know
2ab = 2d, subtract this to get a^2 + b^2
therefore
a^2 + b^2 = 4c^2 - 2d