Find the sum of the geometric series 3+(-6)+...+768

a) -255
b) 513
c) 765
d) -1023​

To solve this problem, we must use the pythagorean theorem. 12 is the hypotenuse or c and 5 is b.

a^2 + (5)^2 = (12)^2. Square the appropriate numbers.

a^2 + 25 = 144. Subtract 25 from each side.

a^2 = 119. Take the square root of each side.

a = √(119). This is only half the value of x. Multiply √(119) by 2

Your answer should be 21.8