Answer:
a[n] = a[n-1]×(4/3)
a[1] = 1/2
Step-by-step explanation:
The terms of a geometric sequence have an initial term and a common ratio. The common ratio multiplies the previous term to get the next one. That sentence describes the recursive relation.
The general explicit term of a geometric sequence is ...
a[n] = a[1]×r^(n-1) . . . . . where a[1] is the first term and r is the common ratio
Comparing this to the expression you are given, you see that ...
a[1] = 1/2
r = 4/3
(You also see that parenthses are missing around the exponent expression, n-1.)
A recursive rule is defined by two things:
- the starting value(s) for the recursive relation
- the recursive relation relating the next term to previous terms
The definition of a geometric sequence tells you the recursive relation is:
<em>the next term is the previous one multiplied by the common ratio</em>.
In math terms, this looks like
a[n] = a[n-1]×r
Using the value of r from above, this becomes ...
a[n] = a[n-1]×(4/3)
Of course, the starting values are the same for the explicit rule and the recursive rule:
a[1] = 1/2
Step-by-step explanation:
the volume of any pyramid is
base area × height / 3
so, since we know the base area (a square with 23 mm side length), the only trick we need to do is to get the inner height (straight up in the middle from the base area to the top of the pyramid).
because this is a regular pyramid (the top of the pyramid is right above the middle of the base area), we can use Pythagoras for right-angled triangles
c² = a² + b²
with c being the Hypotenuse (the baseline of the triangle opposite of the 90° angle) and in our case the outer height along a side area triangle (24 mm).
the legs of that right-angled triangle are half of a base area side length (remember, the top of the pyramid is right over the middle of the base area square) and the inner height to the top.
so, we have
24² = 12.5² + height²
height² = 24² - 12.5² = 576 - 156.25 = 419.75
height = 20.48780125... mm
so, the volume of the pyramid is then
23² × 20.48780125... / 3 = 3,612.682287... mm³ ≈
≈ 3,612.7 mm³
German is correct. hope it helps
