Question

Find the slope intercept form of the line whose slope is 4 and that passes through the point (-7,8) the equation of the line is?

Answer 1

you know that the slope - intercept equation looks like this:

y=mx+b

OK?

Answer 2

Yes...

Answer 3

That's as far as I understand... I don't know how to get the answer.

Answer 4

ok

well the 'm' in that equation is the slope

the question tells oyu the slope

so can you start to write the equation - putting th ecorrect value for m (but leave 'b' for now...)

Answer 5

Y=4x

Answer 6

y = mx +b

m = 4

so write the equation with the value for m in it

Answer 7

(you need the "+b" on the end )

Answer 8

Ok. How do you get b?

Answer 9

Oh, y=4x+b

Answer 10

at the moment I just wanted you to write the equation like this

y = 4x+b

we still need to find b

OK? - we are doing this in 2 steps - you have done one of them so far

Do oyu understand why the equation starts to be

y=4x+b ?

Answer 11

Yes..

Answer 12

OK good

So now the second step is to use the second bit of information from the question

that is the point (-7,8) lise on the line

this means that the equation is true when

x=-7, and y = 8

so write the equation

y = 4x+b

with the values x= -7 and y = 8 in it (leave b as it is for now)

Answer 13

Okay..

Answer 14

so write the equation

y = 4x+b


x= -7
y = 8

in it (leave b as it is for now)

Answer 15

Y=4x+b y =8x=-7 this doesn't make sense to me..

Answer 16

wherever there is y in the equation write 8
wherever there is x write -7 (BUT remember that 4x means 4 times x)

Answer 17

8=4-7+b yes?

Answer 18

B=5

Answer 19

yes - but to be clear about 4 times x it is clearer if oyu write

8 = 4(-7) +b

Answer 20

Y=4(-7)+5. Yes?

Answer 21

yes

so that can be rewritten as
8= -28 +b

so what is b?

Answer 22

Okay.. So I don't need it to equal 5?

Answer 23

B is 5 no??

Answer 24

no it's not , please don't rush - I am trying to guide you to work out the answer

Answer 25

Okay I see..

Answer 26

Sorry..

Answer 27

To review what we did..

we KNOW the equation will be in th eform

y = mx + b

and we know that m is th eslope
and we know the slope is 4

so we know th eequaiton is
y= 4x+b


BUT we also know that the point (-7,8) is on the line (which means the equationis true when it passes through that point)

SO we know that when x = -7 then y = 8

so back to the equation

we put y - 8 and x = -7

so

8=4×(−7)+b


this is the same as

8 = -28 + b

so you can work out b

Answer 28

Yes... B =36

Answer 29

well done

so now write the whole equation
y=mx+b

with the values for m and b that you calculated

Answer 30

Y=4x+36

Answer 31

Correct ?

Answer 32

correct

well done

this is the principle of all these questions -

once you know the slope, you can use 1 point on the line to find b

Answer 33

Thank you sir

Answer 34

So, I attempted my next one and the slope is 7 the point is (-4,11). I came up with y=7x+35 but I was wrong it is 39 and I don't know where I went wrong??

Answer 35

ok you made a good attempt

starting with

y = 7x + b

then we put in the point values

11= 7 (-4) +b

11 = -28 +b

you can see that 39 is the correct value