Question

Someone plz help! Photo Above

Answer 1

• -704

Explanation:

Given the sequence

• A = -4 - 6i

To find

• Sum of terms from i=5 to i=15

Solution

We see the sequence is AP

The required sum is

• S₅₋₁₅ = S₁₅ - S₄

Using sum of AP formula

• Sₙ = 1/2n(i₁ + iₙ)

Finding the required terms

• i₁ = - 4- 6 = -10
• i₄ = -4 -6*4 = - 28
• i₁₅ = -4 -6*15 = -94

Getting the sum

• S₄ = 1/2*4*(-10 - 28) = -76
• S₁₅ = 1/2*15*(-10 - 94) = -780
• S₅₋₁₅ = S₁₅ - S₄ = -780 - (-76) = - 704