Question

If 7 times t7 and 11 times t11 of an ap are equal to t18 is

Answer 1

Answer:

ap = t1,12,13,.... t18

we know that t18 = t + 17d

also it is given that 7(t7 ) = 11 (t11) = t 18

t 7 = t + 6d

t 11 = t + 10d

so, 7( t + 6d ) = 11 ( t + 10d)

7t + 42d = 11t + 110d

7t - 11t = 110d - 42d

-4t = 68d

t = 68d/-4

= -17d

so,

t18 = -17d + 17d

t 18 = 0

Answer 2

t7 = a + 6d

t11 = a + 10d

t18 = a + 17d