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: peter got 11 right and 4 wrong
Step-by-step explanation: So when he answers 11 answers correctly he gains 33 points so he loses 4 points from the remaining 4 wrong answers.
Answer:
Cody has solved (12 × 12) = 144 problems.
Step-by-step explanation:
For every one problem that Julia completes, Cody completes twelve.
If Julia Completes x problems and Cody completes y problems, then we can write y = 12x ........ (1)
Now, given that the number of problems solved by Cody is one hundred twenty more than two times the number of problems solved by Julia.
Hence, 2x + 120 = y ......... (2)
Now, from equations (1) and (2) we get,
2x + 120 = 12x
⇒ 10x = 120
⇒ x = 12
Therefore, Cody has solved (12 × 12) = 144 problems. (Answer)
Answer:
The answer is B. Two Foci, hope this helps! :)
Answer:
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