Answer:
the common ratio is either 2 or -2.
the sum of the first 7 terms is then either 765 or 255
Step-by-step explanation:
a geometric sequence or series of progression (these are the most common names for the same thing) means that every new term of the sequence is created by multiplying the previous term by a constant factor which is called the common ratio.
so,
a1
a2 = a1×f
a3 = a2×f = a1×f²
a4 = a3×f = a1×f³
the problem description here tells us
a3 = 4×a1
and from above we know a3 = a1×f².
so, f² = 4
and therefore the common ratio = f = 2 or -2 (we need to keep that in mind).
again, the problem description tells us
a2 + a4 = 30
a1×f + a1×f³ = 30
for f = 2
a1×2 + a1×2³ = 30
2a1 + 8a1 = 30
10a1 = 30
a1 = 3
for f = -2
a1×-2 + a1×(-2)³ = 30
-10a1 = 30
a1 = -3
the sum of the first n terms of a geometric sequence is
sn = a1×(1 - f^(n+1))/(1-f) for f <>1
so, for f = 2
s7 = 3×(1 - 2⁸)/(1-2) = 3×-255/-1 = 3×255 = 765
for f = -2
s7 = -3×(1 - (-2)⁸)/(1 - -2) = -3×(1-256)/3 = -3×-255/3 =
= -1×-255 = 255
Answer:
2. Sorry, I don't how to put that into words, because i'm trying to use calculators, then figure out how they got their answer.
3. C
Step-by-step explanation:
2. ^
3. to get the difference between two numbers, (100 and 50, for example,) you must just simply have them minus each other, like simple math. 100 - 50 = 50.
So your difference between the number 100, and the number 50, are 50.
<span>So rather than think about how to find the whole numbers, let's try to find the two perfect squares nearest to 38. There is one greater than it and one smaller than it. The square root will lie between the squared value of each. (e.g. 64 is the perfect square, 8 is the squared value i refer to)
</span><span>
6 ,7. 6squared is 36 and 7 squared is 42
therefore 38 lies between these two numbers</span>
