Question

if the sum of 3rd and 11th term is 154 and sum of 6th ad 10th term is 16w find the sum of first 15th term​

Answer 1

Answer:

sorry I don't know the answer........

Answer 2

Answer:

Sum of first 15 terms is 120

Step-by-step explanation:

Sum of 3rd and 11th term is 154

a₃+a₁₁=154

a+2d+a+10d=154

2a+12d=154

a+6d=77 ---->(1)

Sum of 6th and 10th term is 16.

a₆+a₁₀=16

a+5d+a+9d=16

2a+14d=16

a+7d=8 ----->(2)

Subtracting eq(1) from eq(2)

⇒a+7d-a-6d=8-77

⇒d=-69

Substitute in eq(2)

⇒a+7(-69)=8

⇒a=8+483

⇒a=491

Sum of first 15 terms can be given by

S₁₅=$\frac{n}{2}$(2a+(n-1)d)

   =15(2(491)+14(-69))/2

   =15(982-966)/2

   =15(16)/2

    =15(8)

    =120