In an Arithmetic progression,

t15=30,t20=50
Find,
S17=??

In an Arithmetic progression, 

Find S₁₇ ?

Given that;

t₁₅ represents the 15th term of the AP

t₂₀ represents the 20th term of the AP

Now,

We know that;

t₁₅ can be represented as , a + 14d

t₂₀ can be represented as , a + 19d

Now, This implies

Subtract eq 1 from eq 2

a + 19d = 50

a + 14d = 30

(-)(-) (-)

-------------------

0 + 5d = 20

So,

Common difference (d) = 4

Substituting the value of d in eq-1

So,

First term (a) = -26

Now,

Let's find the sum of first 17 terms !

We know that;

Now,

Here the no. of term (n) = 17

We have,

Therefore,

your answer is the frist one

hop i