Question

The 1st term and the 20th term of an A.P whose 5th and 7th terms are 13 and 17 respectively *​

Answer 1

Answer:

a=5

a20 = 43

Step-by-step explanation:

a5 = 13;

a7 = 17;

let the first term be a

Using,

an = a +(n-1)d

a7 = a + 6d

17 = a + 6d........... equation 1

Similarly,

13 = a + 4d........... equation 2

subtracting equation 1 and 2, we get

4 = 2d

so common difference d = 2

Putting d = 2 in equation 1 we get

17 = a + 12

so the first term a = 5

so 20th term

a20 = a + (n-1)d

a20 = 5 + 19d

a20 = 5 + 38

a20 = 43

Hope this one helps you

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Answer 2

explanation:

Hlo muskaan

t5 - 13

t7-17

17=a+6d

13=a+4d

Subtract this equation

a=5

d=2

Thus, t1= 5

t20= 43

Hope this helps u dear !!!