arithmetic
posted by noor on .
If 10 times the 10
th
term of an AP is equal to 15 times its 15
th
term, show that its25
th
term is zero.

T10 = a+9d
T15 = a+14d
10(a+9d) = 15(a+14d)
10a + 90d = 15a + 210d
5a = 120d
a = 24d
T25 = a + 24d = 24d + 24d = 0