Question

Sum of the 5th and 9th terms of an A.P 40 and the sum of 8th and 14th terms is 64 find the first term of 20th sums​

Answer 1

Answer:

Step-by-step explanation:

Answer 2

Answer:

Step-by-step explanation:

a₅=a+4d

a₉=a+8d

a₈=a+7d

a₁₄=a+13d

a+4d+a+8d=40⇒2a+12d=40⇒a+6d=20⇒a=20-6d-(equation-1)

a+7d+a+13d=64⇒2a+20d=64⇒a+10d=32⇒a=32-10d-(equation-2)

equating both the equations for a

20-6d=32-10d⇒4d=12⇒d=3

a=20-6d=20-(6×3)=20-18=2

so a=2 and d=3

Sⁿ=n/2(2a+(n-1)d)

S₂₀=20/2(2×2 + 19×3)=10(4+57)=10×61=610

Sorry if there is any calculation mistake

the methods are all correct

hope this helps you

thank you