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sara
:
the 8th term of an arithmetic progression is 5 times the 4th term.If the second term is -3, find (a) the common difference (b) the first term
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September 14, 2016 at 10:16am
Shu Yun
:
[deqn]a_{n}=a_{1}+(n-1)d\\ since\\ a_{8}=a_{1}+(8-1)d=a_{1}+7d\\ a_{4}=a_{1}+(4-1)d=a_{1}+3d\\ and\\a_{8}=5a_{4}\\a_{1}+7d=5(a_{1}+3d)\\d=-\frac{1}{2}a_{1}-----(1)\\Since\\a_{2}=-3\\ -3=a_{1}+(2-1)d\\-3=a_{1}+d-----(2)\\[/deqn]
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September 14, 2016 at 1:48pm
Shu Yun
:
Solving (1) & (2), a) common difference d=3, b) first term a1= -6
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September 14, 2016 at 1:50pm
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