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
The answer is 10 :) ........
Answer:
Step-by-step explanation:
Since, according to associative property of multiplication,
a(bc) = (ab)c,
Where a, b and c are any real numbers,
Here, the given expression,
2 × ( 5 × 1.5 ),
By applying the associative property of multiplication,
( 2 × 5 ) × 1.5,
Hence, the appropriate expression in the first box is '(2×5)'
And, the appropriate number in the second box is '1.5'.
Answer:
6 of x and 5 of y
Step-by-step explanation:
x = number of closets of the first type
y = number of closets of the second type
1200 = 100x + 120y
100 = 10x + 8y
10x = 100 - 8y
10x(100 - 8y) + 120y = 1200
1000 - 80y + 120y = 1200
40y = 200
y = 5
100 = 10x + 8×5 = 10x + 40
60 = 10x
x = 6
20x + 24y = max
20×6 + 24×5 = 120 + 120 = 240
Step-by-step explanation:
the quotient of a number and 3 is 6
Solution,
Let the number be x, then
