Write the geometric sequence that has five geometric means between 1and 15,625.
I got:
1, 5, 25, 125, 625, 3,125, 15,625, …
is it ok?
3 answers
you are correct if your last numbers are 3125 and 15625.
Partially correct.
Let's the first term in the sequence the 1,
So
a1 = 1
If the ratio between terms is r, then any term in the sequence is :
an = a1 ⋅ r ⁿ⁻¹
If there are 5 geometric means between 1 and 15 625, then 15 625 must be the 7th term ( a7 ).
a7 = 1 ⋅ r⁷⁻¹
15 625 = r⁶
r = ⁶√ 15 625
r = ± 5
a1 = 1
r = 5
a1 = 1 ∙ 5⁰ = 1 ∙ 1 = 1
a2 = 1 ∙ 5¹ = 1 ∙ 5 = 5
a3 = 1 ∙ 5² = 1 ∙ 25 = 25
a4 = 1 ∙ 5³ = 1 ∙ 125 = 125
a5 = 1 ∙ 5⁴ = 1 ∙ 625 = 625
a6 = 1 ∙ 5⁵ = 1 ∙ 3 125 = 3 125
a7 = 1 ∙ 5⁶ = 1 ∙ 15 625 = 15 625
1 , 5 , 25 , 125 , 625 , 3 125 , 15 625
and
a1 = 1
r = - 5
a1 = 1 ∙ ( - 5 )⁰ = 1 ∙ 1 = 1
a2 = 1 ∙ ( - 5 )¹ = 1 ∙ ( - 5 ) = - 5
a3 = 1 ∙ ( - 5 )² = 1 ∙ 25 = 25
a4 = 1 ∙ ( - 5 )³ = 1 ∙ ( -125 ) = - 125
a5 = 1 ∙ ( - 5 )⁴ = 1 ∙ 625 = 625
a6 = 1 ∙ ( - 5 )⁵ = 1 ∙ ( - 3 125 ) = - 3 125
a7 = 1 ∙ ( - 5 )⁶ = 1 ∙ 15 625 = 15 625
1 , - 5 , 25 , - 125 , 625 , - 3125 , 15 625
Let's the first term in the sequence the 1,
So
a1 = 1
If the ratio between terms is r, then any term in the sequence is :
an = a1 ⋅ r ⁿ⁻¹
If there are 5 geometric means between 1 and 15 625, then 15 625 must be the 7th term ( a7 ).
a7 = 1 ⋅ r⁷⁻¹
15 625 = r⁶
r = ⁶√ 15 625
r = ± 5
a1 = 1
r = 5
a1 = 1 ∙ 5⁰ = 1 ∙ 1 = 1
a2 = 1 ∙ 5¹ = 1 ∙ 5 = 5
a3 = 1 ∙ 5² = 1 ∙ 25 = 25
a4 = 1 ∙ 5³ = 1 ∙ 125 = 125
a5 = 1 ∙ 5⁴ = 1 ∙ 625 = 625
a6 = 1 ∙ 5⁵ = 1 ∙ 3 125 = 3 125
a7 = 1 ∙ 5⁶ = 1 ∙ 15 625 = 15 625
1 , 5 , 25 , 125 , 625 , 3 125 , 15 625
and
a1 = 1
r = - 5
a1 = 1 ∙ ( - 5 )⁰ = 1 ∙ 1 = 1
a2 = 1 ∙ ( - 5 )¹ = 1 ∙ ( - 5 ) = - 5
a3 = 1 ∙ ( - 5 )² = 1 ∙ 25 = 25
a4 = 1 ∙ ( - 5 )³ = 1 ∙ ( -125 ) = - 125
a5 = 1 ∙ ( - 5 )⁴ = 1 ∙ 625 = 625
a6 = 1 ∙ ( - 5 )⁵ = 1 ∙ ( - 3 125 ) = - 3 125
a7 = 1 ∙ ( - 5 )⁶ = 1 ∙ 15 625 = 15 625
1 , - 5 , 25 , - 125 , 625 , - 3125 , 15 625
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