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How to find the approximate value of sprt(6)

 Mar 15, 2015

Best Answer 

 #3
avatar+118703 
+10

Yes that is what I was doing Chris, I just didn't halve them because I wanted to do it in my head.  :))

 

Here is another way Sweaty, although it is probably over your head.

You can use calculus and get a lot of accuracy very quickly using

Newton's method of approximating roots.

I derive this formula every time I use it for a have a really bad memory but most people just memorise the formula.

x2=x1f(x1)f(x1)

 

letx=6x2=6x26=0$theideaistolet$f(x)=x26$andsolvefor$y=0f(x)=x26f(x)=2x$thatiscalculus$$nowweknowthat$2$Somyfirstestimatewillbe$x1=2.5x2=2.52.52622.5x2=2.45

 

\\\mbox{second use of the formula}\\\\  x_3=2.45-\frac{2.45^2-6}{2*2.45}\\\\  x_3=\textcolor[rgb]{1,0,0}{\mathbf{2.449489796}}\\\\  $third use of the formula$\\\\  x_4=2.449489796-\frac{2.449489796^2-6}{2*2.449489796}\\\\  x_4=\textcolor[rgb]{1,0,0}{\mathbf{2.449510072}}\\\\  $The value is already correct to 4 decimal places }  \sqrt{6}=2.4495\\\\\\  $With each iteration the accuracy will increase.$

 

You will learn and understand this when you do calculus - something to look forward too :))

 Mar 15, 2015
 #1
avatar+118703 
+10

Well there would be a number of ways Sweatie.  The easiest one is to use a calculator.

 

This is another way:

You know it is between 2 and 3

2<6<3

 

2.52=6.25$thatistoobig$2<6<2.52.32=5.29$toosmall$2.3<6<2.52.42=5.76$toosmall$2.4<6<2.5etc

 

you can continue to do this untill you get the accuracy that you need.

 

Note: I did not use a calculator at all for what I have done so far there.

This is an incite into how I do it. :)

232=(20+3)2=400+2320+9=400+120+9=529so2.32=5.29$Icandothatinmyheadwithpracticeyoucouldtoo.:)$

 Mar 15, 2015
 #2
avatar+130477 
+10

Here is a method that is similar to Melody's...it converges pretty fast....even if our intial guess is not too good.

This method is known as "Guess - Divide - Check "

Step 1  : Let's say that we guess the square root of 6 as 2

Step 2 : Divide 6 by 2  = 3

Step 3 :  Now add 2 +3  and divide by 2 = 2.5

Step 4: Now divide 6 by 2.5 = 2.4

Step 5: Now add 2.5 and 2.4 and divide by 2 = 2.45

Step 6 :  Divide 6 by 2.45 = 2.448

Step 7 : Add 2.448 and 2.45 and divide by 2 = 2.449

Step 8: Divide 6 by 2.449 = 2.449......note this is pretty close to the actual square root of 6 !!!

 

This isn't hard to do.....once you get the "rhythm" down.....!!!!......with a better initial guess.....the procedure may have even converged much more quickly!!!

 P.S.  -  The method might be better termed as "Guess - Divide - Average - Divide - Average - Divide......."

  

 Mar 15, 2015
 #3
avatar+118703 
+10
Best Answer

Yes that is what I was doing Chris, I just didn't halve them because I wanted to do it in my head.  :))

 

Here is another way Sweaty, although it is probably over your head.

You can use calculus and get a lot of accuracy very quickly using

Newton's method of approximating roots.

I derive this formula every time I use it for a have a really bad memory but most people just memorise the formula.

x2=x1f(x1)f(x1)

 

letx=6x2=6x26=0$theideaistolet$f(x)=x26$andsolvefor$y=0f(x)=x26f(x)=2x$thatiscalculus$$nowweknowthat$2$Somyfirstestimatewillbe$x1=2.5x2=2.52.52622.5x2=2.45

 

\\\mbox{second use of the formula}\\\\  x_3=2.45-\frac{2.45^2-6}{2*2.45}\\\\  x_3=\textcolor[rgb]{1,0,0}{\mathbf{2.449489796}}\\\\  $third use of the formula$\\\\  x_4=2.449489796-\frac{2.449489796^2-6}{2*2.449489796}\\\\  x_4=\textcolor[rgb]{1,0,0}{\mathbf{2.449510072}}\\\\  $The value is already correct to 4 decimal places }  \sqrt{6}=2.4495\\\\\\  $With each iteration the accuracy will increase.$

 

You will learn and understand this when you do calculus - something to look forward too :))

Melody Mar 15, 2015
 #4
avatar+118703 
0

Thanks Chris :))

 Mar 15, 2015

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