Question 1080880: the 3rd,5th and 8th terms of a n arithmetical progression are 3x+8,x+24,x^3+15 respectively .Find the value of x and common difference
Answer by Boreal(15235)   (Show Source):
You can put this solution on YOUR website! Twice the difference is between the third and fifth, and that difference is x+24-(3x+8)=-2x+16.
So, the common difference is -x+8.
Between the fifth and eight is 3(-x+8)=-3x+24, and that plus x+24=x^3+15.
x^3+15=-2x+48
x^3+2x-33=0
graph it and x=3. Common difference is -6+16=10, between 3 and 5, so half of that is 5 ANSWER.
check between 5 and 8, where there should be a difference of 15.
x^3+15-(x+24)=x^3-x-9=15
Check between 3 and 8, where there should be a difference of 25
x^3+15-(3x+8)=x^3-3x+7=25
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