SOLUTION: Make a conjecture about the following results: Square root of 2 2/3=2 square root of 2/3. Square root of 3 3/8=3 square root of 3/8. Try to prove your conjecture.

Algebra ->  Divisibility and Prime Numbers -> SOLUTION: Make a conjecture about the following results: Square root of 2 2/3=2 square root of 2/3. Square root of 3 3/8=3 square root of 3/8. Try to prove your conjecture.       Log On


   



Question 846438: Make a conjecture about the following results:
Square root of 2 2/3=2 square root of 2/3.
Square root of 3 3/8=3 square root of 3/8.
Try to prove your conjecture.

Answer by Edwin McCravy(20060) About Me  (Show Source):
You can put this solution on YOUR website!
Square root of 2 2/3=2 square root of 2/3.
Square root of 3 3/8=3 square root of 3/8.
sqrt%282%262%2F3%29%22%22=%22%22sqrt%288%2F3%29%22%22=%22%22sqrt%284%2A2%2F3%29%22%22=%22%22sqrt%284%2Aexpr%282%2F3%29%29%22%22=%22%222%2Asqrt%282%2F3%29

sqrt%283%263%2F8%29%22%22=%22%22sqrt%2827%2F8%29%22%22=%22%22sqrt%289%2A3%2F8%29%22%22=%22%22sqrt%289%2Aexpr%283%2F8%29%29%22%22=%22%223%2Asqrt%283%2F8%29

It's easy to see the pattern, except for the denominators, where
I have put question marks below.  There is no way to determine just by
inspection, a sequence for the denominators with just the first 
two terms, 3 and 8.  We could guess a general term for the
denominators, but that would be risky business. 

sqrt%28n%2Bn%2F%22%3F%22%29%22%22=%22%22n%2Asqrt%28n%2F%22%3F%22%29 

Now let's let D be those denominators, 

sqrt%28n%2Bn%2FD%29%22%22=%22%22n%2Asqrt%28n%2FD%29

and solve for D.  Square both sides:

n%22%22%2B%22%22n%2FD %22%22=%22%22 n%5E2%2A%28n%2FD%29

%28nD%2Bn%29%2FD%22%22=%22%22n%5E3%2FD

Multiply both sides by D

nD%2Bn%22%22=%22%22n%5E3

Divide through by n

D%2B1%22%22=%22%22%22%22=%22%22n%5E2

D%22%22=%22%22n%5E2-1 for n > 1

So our conjecture is found by substituting that
expression for D in:

sqrt%28n%2Bn%2FD%29%22%22=%22%22n%2Asqrt%28n%2FD%29

sqrt%28n%2Bn%2F%28n%5E2-1%29%29%22%22=%22%22n%2Asqrt%28n%2F%28n%5E2-1%29%29 for n > 1

To prove that we have to show that each side is non-
negative (obvious) and have the same square.  We show 
that each side has the same square:

LEFT SIDE = sqrt%28n%2Bn%2F%28n%5E2-1%29%29%22%22=%22%22

SQUARE OF LEFT SIDE = n%2Bn%2F%28n%5E2-1%29%22%22=%22%22%28n%5E3-n%2Bn%29%2F%28n%5E2-1%29%22%22=%22%22n%5E3%2F%28n%5E2-1%29

RIGHT SIDE = n%2Asqrt%28n%2F%28n%5E2-1%29%29

SQUARE OF RIGHT SIDE = n%5E2%28n%2F%28n%5E2-1%29%29%22%22=%22%22n%5E3%2F%28n%5E2-1%29

So they have the same square and are both non-negative so the conjecture
is proved.

Edwin