Finding points on a line from user input

The question is as follows: 'Make a function file “e82.m” with 5 input parameters. The first four are two pairs of xand y- coordinates (x1, y1, x2, y2 ) and the fifth, a single x-value. The first four are two dots in a y-x plot. Connect these with a line and the fifth value is also a dot on the same line, but you should find out the corresponding y-value and present everything in a plot. Of course the five parameters must be chosen to be arbitrary.'

so far I have this: xvalueone = 'x value between 0 and 10'; xvalue = input(xvalueone); a=xvalue/10

yvalueone = 'y value between 0 and 10'; yvalue = input(yvalueone); b=yvalue/10

xvaluetwo = 'second x value between 0 and 10'; xvalue = input(xvaluetwo); c=xvalue/10

yvaluetwo = 'second y value between 0 and 10'; yvalue = input(yvaluetwo); d=yvalue/10

A=[a,c] B=[b,d]

plot(A,B,'-')

input ('select x value between the previous two values')

BUT I don't know how to get the corresponding value from the line.

Thanks for any help

Answer 1

[Image Analyst]

Use the equation of a line y = m*x+b. m is the slope and is (y2-y1)/(x2-x1). b is the offset and I'm sure you can figure that out because this is just 8th grade algebra. If you can't, you can just use polyfit to tell you.

coeffs = polyfit([x1, x2], [y1, y2], 1)

So then you know m, and b, and you just plug in the x and you get the y - it's trivial.

Answer 2

[Brian]

Thanks...in all these problems it isn't the maths that causes problems I just don't know how to programme what I want to, I never did anything before/other languages.