Question

the third and seventh term of an ap are 18and 30 respectively find the sum of their 17 term​

Answer 1

Step-by-step explanation:

given,

a3=18, a7=30

a3=18

a+2d=18 (eq-1)

a7=30

a+6d=30 (eq-2)

by elimination method

subtarcting eq-1 from eq-2

a + 6d = 30

a + 2d = 18

- - -

0 4d = 12

d=12÷4

d=3

putting the value of d in eq 1

a+2×3=18

a=18-6

a=12

now sum,

n=17

sum=17/2[2×12+(17-1)(3) ]

=17/2[24+48]

=17/2[52]

=17×26

=442

Answer 2

Step-by-step explanation:

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