Answer:
<em>u</em> = 7.21
Step-by-step explanation:
The magnitude of <em>u</em> is just the distance between the two points. The coordinates of the left-most point are (-2,-8) and the coordinates of the right point are (4, -4). I'm assuming the x coordinates here because we don't actually know the scale.
Ok so from these points, you can draw a triangle (u can see it in the attached file).
From the coordinates we can tell the lengths of the sides, and the triangle shows that <em>u</em> is the hypotenuse of the triangle. This triangle is also a right triangle, so u can use Pythagoras' theorem to find the length of <em>u</em>.

Since c = <em>u</em>, we know now that the magnitude of <em>u</em> is 7.21
Hope this helps!
Hey ok, let me work this problem out, could u give me the formal?
i cant find the notes so i need the formal.
A=84 and r=1/5
Since r, the common ratio squared is less than one, the sum will converge to a limit. Rule: if r^2<1 infinite series converges, otherwise it diverges.
Since the sum of any geometric sequence is:
s(n)=a(1-r^n)/(1-r)
And if r^2<1, (1-r^n) becomes 1-0=1 as n approaches infinity.
So whenever r^2<1 the sum of the infinite series is just:
s(n)=a/(1-r)
Since a=84 and r=1/5 this infinite series has a sum of:
s(n)=84/(1-1/5)
s(n)=84/(4/5)
s(n)=5(84)/4
s(n)=105