Question

if 6 term of an ap is -10 and its 10th term of is - 26 then find the 15 terms of an ap

Answer 1

a6=a+(n-1)d
-10=a+(6-1)d
-10=a+5d

a10=a+(n-1)d
-26=a+(10-1)d
-26=a+9d

a+5d=-10---->[1]
a+9d=-26----->[2]
(-) (-) (+)
________
-4d=16
d=16/-4
d=-4

put d=-4 in (1)
a+5 (-4)=-10
a-20=-10
a=-10+20
a=10

a15=a+(n-1)d
=10+(15-1)-4
=10+14×(-4)
=10-56
=-46