SOLUTION: -the 4th term of an AP is 7 and the 9th term is 17 find the 15th term ?? -if 4 times the 4th term of an AP is equal to 7 times the 7th term,find its 11th term

Algebra ->  Sequences-and-series -> SOLUTION: -the 4th term of an AP is 7 and the 9th term is 17 find the 15th term ?? -if 4 times the 4th term of an AP is equal to 7 times the 7th term,find its 11th term       Log On


   

Question 843458: -the 4th term of an AP is 7 and the 9th term is 17 find the 15th term ??
-if 4 times the 4th term of an AP is equal to 7 times the 7th term,find its 11th term
Found 2 solutions by TheInstructor, mathgenboy:
Answer by TheInstructor(29) About Me  (Show Source):
You can put this solution on YOUR website!
Hey!
T4= a+3d =7 ----- (1)
T9= a+8d =17 ----- (2)
(2)-(1)
Therefore 5d = 10
d=2

a+ 6= 7
Therefore a = 1
T15= a+14d
T15 = 1 + 14(2) = 29

Answer by mathgenboy(3) About Me  (Show Source):
You can put this solution on YOUR website!
The second question: Interpreting the question
4+%2A+4th=7+%2A+7th4%2A%28a%2B+3d%29=7%2A%28a%2B+7d4a%2B+12d=7a%2B+49d
collect like terms4a-7a=49d-12d-3a=30d divide both sides by -3, then a=-10d. Now 11th=a%2B+10dsubstitute a=-10d, then 11th=-10d+%2B+10d. Therefore 11th=0