+0  
 
0
1232
1
avatar

The equation x3 + 2x = 26 has a solution between 2 and 3. Use a trial and improvement method to find this solution. Give your answer correct to one decimal place.

 May 20, 2015

Best Answer 

 #1
avatar+129839 
+5

x^3 + 2x - 26 = 0     let us guess that the root is 2.5

(2.5)^3 + 2(2.5) - 26 = -5.375     we kmow that the root must be between this and 3......add 3 + 2.5 and divide by 2  = 2.75

Let's test this   (2.75)^3 + 2(2.75) - 26 = 0.296875  .....now we know that the root is between 2.5 and 2.75.....continuing the same process  (2.5+ 2.75) / 2 =  2.625

(2.625)^3 + 2(2.625) - 26 = -2.662109375...and the root lies between this and 2.75

(2.625 + 2.75)/2 = 2.6875

(2.6875)^3 + 2(2.6875) - 26 = -1.214111328125   .....now we know that the root lies between 2.6875 and 2.75  ....so (2.6875 + 2.75) / 2 = 2.71875

(2.71875)^3 + 2(2.71875) -26 = -0.466583251953125.....and the root still lies between this and 2.75

(2.71875 + 2.75) /2 = 2.734375

(2.734375 )^3 + 2(2.734375) - 26 = -0.0868568420410156.....and the root still lies between this and 2.75

(2.734375 + 2.75)/ 2 = 2.7421875

(2.7421875)^3 + 2(2.7421875) - 26 = 0.1045069694519043.....and the root lies between this and 2.734375

(2.734375 + 2.7421875) / 2  = 2.73828125

(2.73828125)^3 + 2(2.73828125) - 26 = 0.0086997151374817...this is pretty close to 0.....

The actual root is about 2.737.......this is way more than the problem required...this just demonstrates that this process can be tedious...........

 

 

 May 20, 2015
 #1
avatar+129839 
+5
Best Answer

x^3 + 2x - 26 = 0     let us guess that the root is 2.5

(2.5)^3 + 2(2.5) - 26 = -5.375     we kmow that the root must be between this and 3......add 3 + 2.5 and divide by 2  = 2.75

Let's test this   (2.75)^3 + 2(2.75) - 26 = 0.296875  .....now we know that the root is between 2.5 and 2.75.....continuing the same process  (2.5+ 2.75) / 2 =  2.625

(2.625)^3 + 2(2.625) - 26 = -2.662109375...and the root lies between this and 2.75

(2.625 + 2.75)/2 = 2.6875

(2.6875)^3 + 2(2.6875) - 26 = -1.214111328125   .....now we know that the root lies between 2.6875 and 2.75  ....so (2.6875 + 2.75) / 2 = 2.71875

(2.71875)^3 + 2(2.71875) -26 = -0.466583251953125.....and the root still lies between this and 2.75

(2.71875 + 2.75) /2 = 2.734375

(2.734375 )^3 + 2(2.734375) - 26 = -0.0868568420410156.....and the root still lies between this and 2.75

(2.734375 + 2.75)/ 2 = 2.7421875

(2.7421875)^3 + 2(2.7421875) - 26 = 0.1045069694519043.....and the root lies between this and 2.734375

(2.734375 + 2.7421875) / 2  = 2.73828125

(2.73828125)^3 + 2(2.73828125) - 26 = 0.0086997151374817...this is pretty close to 0.....

The actual root is about 2.737.......this is way more than the problem required...this just demonstrates that this process can be tedious...........

 

 

CPhill May 20, 2015

2 Online Users

avatar
avatar