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# Math help @CPhill and Melody

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http://papers.xtremepapers.com/CIE/Cambridge%20IGCSE/Mathematics%20(0580)/0580_s11_qp_22.pdf

Help me in question number 18

Jan 21, 2017

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and how did u get the y intercept

Jan 21, 2017

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Let see

A(7,0)    B(5,3)

Midpoint of AB = $$(\frac{7+5}{2},\frac{0+3}{2})=(6,1.5)$$

equation of CB

The y intersept is 4      b=4

Draw in the right angled triangle between the points B and C and you can see  the gradient m

i.e.

$$m=\frac{rise}{run}=\frac{-1}{5}$$

so the equation of BC is

$$y=\frac{-1}{5}x+4\\ y=\frac{-x}{5}+4\\$$

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Jan 21, 2017
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Can u tell me the general formula for the midpoint in terms of x and y

Rauhan  Jan 21, 2017
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and how did u get the y intercept

Rauhan  Jan 21, 2017
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The midpint is just (the average of the 2 x values, the average of the 2 y values)

To get the average of 2 numbers you add them together and divide by 2

So the average of 12 and 5 for instance is   (12+5)/2 = 17/2 = 8.5

If you want the more formal look,

The mid point of

$$(x_1,y_1)\;\;and\;\;(x_2,y_2) \;\;is\;\;\;\;(\frac{x_1+x_2}{2},\frac{y_1+y_2}{2})$$

The y intercept is where the line crosses the y axis and you can see that it crosses at  4

SO the y intercept, which is always given the letter b =4

Melody  Jan 21, 2017