it would be da families with 1 child
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:
x = - 
, x = 3
Step-by-step explanation:
Given
(4x - 5)² = 49 ( take the square root of both sides )
4x - 5 = ± 
= ± 7 ( add 5 to both sides )
4x = 5 ± 7, thus
4x = 5 - 7 = - 2 ( divide both sides by 4 )
x = 
= -
or
4x = 5 + 7 = 12 ( divide both sides by 4 )
x = 3
As a check
Substitute these values into the left side of the equation and if equal to the right side then they are the solutions.
x = -
left side = (- 2 - 5)² = (- 7)² = 49 = right side ⇒ solution
x = 3
left side = (12 - 5)² = 7² = 49 = right side ⇒ solution
Answer: 9
Step-by-step explanation: process of elimination
Answer:
x=4/3
Step-by-step explanation:
