Help With Question needed (1 Viewer)

[ssukarieh1]

This question is from the Cambridge yr 11 2 Unit textbook.

This question comes from the section regarding only the formula for the nth term of an A.P.

Q10. B) The fourth, sixth and eighth terms of an AP add to -6. What is the eighth term?

Help is much appreciated!

 

[enigma_1]

This question is from the Cambridge yr 11 2 Unit textbook.

This question comes from the section regarding only the formula for the nth term of an A.P.

Q10. B) The fourth, sixth and eighth terms of an AP add to

Formula for nth term of an AP is Tn=a+(n-1)d

For fourth term it is: a+(4-1)d
= a+3d

For sixth term it's: a+ (6-1)d
= a+5d

Similarly, for eight term it is
= a+7d

Adding all

a+3d+a+5d+a+7d=-6
3a+15d=-6

Simplifying it down by dividing all terms by 3 gives you

a+5d=-2

If we put this back into the Tn format, it's a+(n-1)d
so a+(6-5)d
hence n is 6 in this case. Meaning that that sixth term of the AP is -2

Wait ok there's no way to find the eighth term...are you sure they're asking for 8th term? I think it should probs be 6th..

 

[ssukarieh1]

Yep, my mistake it asked for the sixth term! Thank you very much, much appreciated

 

[enigma_1]

no probs