Answer:
Step-by-step explanation:
<u>Given the sequence</u>
<u>To find </u>
- Sum of terms from i=5 to i=15
<h3>Solution</h3>
We see the sequence is AP
<u>The required sum is</u>
<u>Using sum of AP formula</u>
<u>Finding the required terms</u>
- i₁ = - 4- 6 = -10
- i₄ = -4 -6*4 = - 28
- i₁₅ = -4 -6*15 = -94
<u>Getting the sum</u>
- S₄ = 1/2*4*(-10 - 28) = -76
- S₁₅ = 1/2*15*(-10 - 94) = -780
- S₅₋₁₅ = S₁₅ - S₄ = -780 - (-76) = - 704
Your sister would be 66.
When you are 10, your sister would be 6 (10-4=6)
60 years later, you would be 70, and your sister would still be 4 years younger.
-6z = 72
Divide both sides by -6
-6z = 72
/-6 /-6
z = -12
