Posted by Anonymous on Sunday, February 21, 2010 at 8:10am.
three number form an arithmetric sequence. Their sum is 24.
A)If 'a' is the first number and 'd' the common difference, show that a+d=8
B)If the first number is decreased by 1 and the second number by 2, the three numbers then form a geometric sequence. Find the three terms.
- maths - Reiny, Sunday, February 21, 2010 at 8:39am
your last 3 postings all deal with the basic definitions of sequences and series and involve translating the English statements into mathematical expressions.
Why don't you show me what you have done for this one so far, and I will gladly help you further.
- maths - Anonymous, Sunday, February 21, 2010 at 8:49am
ok cool... a) S/n=n/2 [2a+(n-1)d]
B)i dont know from here hey...
my name is marco
- maths - Reiny, Sunday, February 21, 2010 at 9:02am
ok Marko, it would have been easier to just do this
a + a+d + a+2d = 24
3a + 3d = 24
a + d = 8
b) so now we know that a = 8-d
"If the first number is decreased by 1" so term1 = a-1
" the second number by 2" , so term2 = a+d - 2
our new terms are then
t1 = a-1 = 8-d - 1 = 7-d
t2 = a+d-2 = 8-d-d-2 = 6
t3 = a+2d = 8-d + 2d = 8+d
now these form a GS
6/(7-d) = (8+d)/6
- correction - maths - Reiny, Sunday, February 21, 2010 at 9:05am
near the end I had a typo but it did not cause an error
t2 = a+d-2 = 8-d-d-2 = 6 should have been
t2 = a+d-2 = 8-d+d-2 = 6
- maths - Anonymous, Sunday, February 21, 2010 at 9:20am
ok thx.. i got 36=(8+d)(7-d)
36= 56-8d+7d-d squared
- maths - Reiny, Sunday, February 21, 2010 at 9:38am
Nice, see how easy they are ?
- maths - Anonymous, Sunday, February 21, 2010 at 10:13am
ya thx a ton
Answer this Question
More Related Questions
- maths - In the sequence: x+4y ; 2y+2 ;x ;y-1, (consisting of 4 terms) the first ...
- Calculus Infinite Geometric Series - So this is what Im basically doing, I got ...
- math - Three numbers in an arithmetic sequence sum to six. If you add 1 to the ...
- algebra - Twice the first number is eleven more than the sum of the other two ...
- Math - The first three elements of a number sequence are 1, 2, 3. ( As you can ...
- 6th grade math - Can you check these problems, please? Translate each phrase ...
- MATH - the first number of a sequence is 200. every number of the sequence after...
- math - the first number of a sequence is 200. every number of the sequence after...
- Grade 8 Math - Can you write them in Mathematical/numbers form I'll solve them ...
- MATH - A new sequence is formed by adding together the corresponding terms of a ...