Question

if s10 =55 and s9=45 find a10​

Answer 1

Answer:

10

Step-by-step explanation:

S10-S9=A10

therefore a10 = 10  (55-45)

Answer 2

Step-by-step explanation:

Sn= n/2[2a+(n-1)d]

S10=10/2[2a+(10-1)•d]

S10=5[2a+9d] =55‐--‐(i)

S10=2a+9d=55/5=11(by taking 5 to RHS)

Now,

S9=9/2[2a+(9-1)d]=45

S9=2a+8d=45/4.5=10--------(ii)

Then,subtracting both equations

2a+9d=11

-2a+8d=10

---------------

1d=1

Substitute the value in equation (i)

2a+9•1=11

2a=11-9=2

a=2/2=1

Now = a10=a+(n-1)d

a10= 1+(10-1)1

a10=1+9=10 (ans)