midpoint issue

**anthonye** · December 14th 2011, 05:58 AM

Hi;
Can someone just tell me the midpoint of

-pi/6 and 5pi/6

Thanks.

**e^(i*pi)** · December 14th 2011, 06:02 AM

Originally Posted by anthonye

Hi;
Can someone just tell me the midpoint of

-pi/6 and 5pi/6

Thanks.

Their midpoint is the same as their mean in this case so add them and divide by 2. You should get $\frac{\pi}{3}$

**anthonye** · December 14th 2011, 06:04 AM

Yeah thanks thats what I get. the web gets pi/2 thought I was right.

**anthonye** · December 14th 2011, 06:07 AM

so in this case pi/3 and 5pi/7 I get 7pi/12.

**e^(i*pi)** · December 14th 2011, 06:20 AM

Originally Posted by anthonye

so in this case pi/3 and 5pi/7 I get 7pi/12.

I get $\dfrac{11\pi}{21}$ . I'm not sure how you got to twelfths from twenty-firsts (21 being the LCD of 3 and 7)

Spoiler:

More generally lets say you have a line between $a$ and $b$ and you want to find the midpoint (we'll call this $c$ ). By definition the midpoint (c) is equidistant from either end (a and b). Thus $b - c = c - a$ .

With a little bit of manipulation: $b+a = 2c$ and $c = \dfrac{b+a}{2}$ . This is the same as the (arithmetic) mean of a and b.

**earboth** · December 14th 2011, 06:25 AM

Originally Posted by anthonye

Yeah thanks thats what I get. the web gets pi/2 thought I was right.

Seems to be a sign mistake because: $\frac{+\frac \pi6+\frac56 \pi}2=\frac \pi2$

Originally Posted by anthonye

so in this case pi/3 and 5pi/7 I get 7pi/12.

How did you get this result?

$\frac{\frac \pi3 + \frac57 \pi}2=\frac{\frac7{21} \pi+\frac{15}{21} \pi}2$

which will never yields your result.

**anthonye** · December 14th 2011, 06:29 AM

Oops sorry wrote it wrong it should be

pi/3 and 5pi/6 gives 7pi/6 then dived by 2 for midpoint 7pi/12.

**e^(i*pi)** · December 14th 2011, 06:32 AM

Originally Posted by anthonye

Oops sorry wrote it wrong it should be

pi/3 and 5pi/6 gives 7pi/6 then dived by 2 for midpoint 7pi/12.

Yes, that's right

**anthonye** · December 14th 2011, 06:35 AM

Thanks.

**anthonye** · December 14th 2011, 08:38 AM

This is all to do with setting up the axis for a sing graph when my midpoint is pi/3.

this is the first point after the origin should'nt it be pi/6 to match the phase shift which is -pi/6.

**anthonye** · December 17th 2011, 08:20 AM

I am right about the phase shift.

y=3sin2(x + pi/6).

Thanks.

**HallsofIvy** · December 21st 2011, 03:32 AM

Originally Posted by anthonye

Yeah thanks thats what I get. the web gets pi/2 thought I was right.

$\pi/2$ is the midpoint of + $\pi/6$ and $5\pi/6$ .

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