Answer:
Option A. 5
Step-by-step explanation:
From the question given above, the following data were obtained:
First term (a) = –3
Common ratio (r) = 6
Sum of series (Sₙ) = –4665
Number of term (n) =?
The number of terms in the series can be obtained as follow:
Sₙ = a[rⁿ – 1] / r – 1
–4665 = –3[6ⁿ – 1] / 6 – 1
–4665 = –3[6ⁿ – 1] / 5
Cross multiply
–4665 × 5 = –3[6ⁿ – 1]
–23325 = –3[6ⁿ – 1]
Divide both side by –3
–23325 / –3 = 6ⁿ – 1
7775 = 6ⁿ – 1
Collect like terms
7775 + 1 = 6ⁿ
7776 = 6ⁿ
Express 7776 in index form with 6 as the base
6⁵ = 6ⁿ
n = 5
Thus, the number of terms in the geometric series is 5.
Remark
It's a right triangle so the Pythagorean Theorem applies. All you have to do is put the right things in the right places of the formula.
Givens
a = x
b = x + 4
c = 20
Formula and Substitution.
a^2 + b^2 = c^2
x^2 + (x + 4)^2 = 20^2
Solution
x^2 + x^2 + 8x + 16 = 20 Collect the like terms on the left.
2x^2 + 8x + 16 = 20 Subtract 20 from both sides.
2x^2 + 8x + 16 - 20 = 0
2x^2 + 8x - 4 = 0 Divide through by 2
x^2 + 4x - 2 = 0
Use the quadratic formula
a = 1
b = 4
c = - 2

From which x = (-4 +/- sqrt(24) ) / 2
x1 = (- 4 +/- sqrt(4*6) ) / 2
x1 = (- 4 +/- 2 sqrt(6) ) / 2
x1 = -2 + sqrt(6)
x2 = -2 - sqrt(6) This is an extraneous root. No line can be minus.
x1 = + 0.4495
x2 = x + 4 = 4.4495
Try to just put 10 or =10
The diameter of the circle is needed. But to solve, you would simply multiply the diameter of the circle by pi (3.14).