If a3=15,S10=125, find d and a10
Given: a3=15,S10=125
⇒a3=15
⇒a+2d=15
⇒a=15−2d ------------- (1)
Now,
⇒s10=125
⇒125=102[2a+(n−1)d]
⇒125=5[2(15−2d)+(10−1)d] [Using eq.(1)]
⇒1255=30−4d+9d
⇒25=30+5d
⇒25−30=5d
⇒−5=5d
⇒d=−1
From (1), we have
⇒a=15−2×−1=17
Hence, a10=a+9d=17−9=8