Author Topic: Sequences and Series Question? (Read 1538 times) Tweet Share

wildareal · « **on:** March 24, 2010, 06:51:11 pm »

The side lengths of a right-angled triangle form the successive terms of an arithmetic sequence. The perimeter of the triangle is 72m. What are the side length of the triangle?

the.watchman · « **Reply #1 on:** March 24, 2010, 07:04:53 pm »

$x^2 + (x-d)^2 = (x+d)^2$

AND $x+x+d+x-d = 72$ , $3x=72$ , $x=24$

So $24^2 + (24-d)^2 = (24+d)^2$

$1152-48d+d^2 = d^2 + 48d + 576$ , $d=6$

SO the lengths are 18m, 24m and 30m

wildareal · « **Reply #2 on:** March 24, 2010, 07:21:28 pm »

Very Nice. I was beginning to do it like that today, but my teacher told me to do it using the tn and Sn formulae. You end up getting two equations but with 3 unknowns. Btw I reckon you should aim your ENTER 99+!

the.watchman · « **Reply #3 on:** March 24, 2010, 07:26:17 pm »

Well after the first step, you could do:

AND $S_3 = \frac{3}{2}(t_1 + t_3) = 72$

$\frac{3}{2}(x-d + x+d) = 72$

$3x=72$ , $x=24$

ETC.

vea · « **Reply #4 on:** March 24, 2010, 08:05:58 pm »

Quote from: wildareal on March 24, 2010, 07:21:28 pm

Very Nice. I was beginning to do it like that today, but my teacher told me to do it using the tn and Sn formulae. You end up getting two equations but with 3 unknowns. Btw I reckon you should aim your ENTER 99+!

Genius...the guy is a genius

the.watchman · « **Reply #5 on:** March 24, 2010, 10:25:45 pm »

Quote from: vea on March 24, 2010, 08:05:58 pm

Quote from: wildareal on March 24, 2010, 07:21:28 pm
Very Nice. I was beginning to do it like that today, but my teacher told me to do it using the tn and Sn formulae. You end up getting two equations but with 3 unknowns. Btw I reckon you should aim your ENTER 99+!

Genius...the guy is a genius

Nah, I just listen hard in class

But no my ATAR aim is MY ATAR aim

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Author Topic: Sequences and Series Question? (Read 1538 times) Tweet Share

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