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junior college 1 | H2 Maths
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Amy Ang
Amy Ang

junior college 1 chevron_right H2 Maths chevron_right Singapore

can help solve? not sure if it’s my morning brain or what but I can’t solve these 2...

Date Posted: 4 years ago
Views: 546

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Matthew Fan
Matthew Fan's answer
39 answers (A Helpful Person)
1st
The key is to realise u_n is an arithmetic progression
J
J
4 years ago
First part actually no need to find un. Just take SN - S4

N(N+14)/3 - 4(4+14)/3

= (N² + 14N)/3 - 24

Since the sum formula already given
Matthew Fan
Matthew Fan
4 years ago
That is right, yes the solution can be made much shorter that way
Amy Ang
Amy Ang
4 years ago
thanks!
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Matthew Fan
Matthew Fan's answer
39 answers (A Helpful Person)
And this is the second question. Time for some self-advertising: Im offering free trial of online lessons. If interested, approach me at 8533 3271