Question

given a3=15,S10=125,find d and a10.​

Answer 1

Answer:

a3=15

we know that an=a+(n-1)d

therefore a+(3-2)d=15

a+2d=15

a=15-2d -‐‐----------(1)

S10=125

we know that sn=n/2(2a+(n-1)d)

therefore

10/2[2a+(10-1)d]=125

5[2a+9d]=125--------------(2)

Putting the value of equation 1 in equation 2

5[2(15-2d)+9d]=125

[30-4d+9d]=125/5

[30+5d]=25

5d=25-30

5d=-5

d= -1)

Therefore,d = -1

Putting the value of d in equation (1)

a=15-2d

a=15-2(-1)

a=15+2

a=17

a10=a+(10-1)d

a10=a+9d

Putting the value of a and d

a10= 17+9(-1)

a10= 17-9

a10= 8