if in a ap the 11th term is -30 and 21st term is -70 find the 21st term
Answers
Answered by
1
Step-by-step explanation:
a+ 10d= - 30........(1)
a + 20 d = -70 .. (2)
-30 -10d +20 d = -70
10d = -40
d = - 4
a= 10
Answered by
2
Answer:
Step-by-step explanation:
nth term of AP is given by tₙ = a + (n-1)d
11th term of AP = a + (11 - 1)d = - 30
=> a + 10d = - 30 -------------------- (1)
21st term of AP = a + (21 - 1)d = - 70
=> a + 20d = - 70 -------------------- (2)
Subtract (1) from (2)
a + 20d = -70
a + 10d = -30
- - +
-------------------------
10d = - 40
=> d = -4.
Substitute value back in (1),
a + 20(-4) = -70
=> a = -70 + 80 = 10.
now you can find the required term.
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