How do you find the equation of a line that Contains point (-1, 2) and is parallel to x-2y=-3?

1 Answer
Jun 17, 2016

ul("Every step shown. With practice a lot of these can be done in the head.")

y=1/2x+2 1/2

Explanation:

Method:
Convert the given equation into standard form for ease of recognition.

Use the given information to determine the equation of the new line.
'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
color(red)("Converting the equation into standard form")

color(green)("Step 1")

Given: color(brown)(x-2y=-3)

Subtract color(blue)(x) from both sides (isolates the term with y in it)

" "color(brown)(x color(blue)(-x)-2y" "=" "-3color(blue)(-x))

" "0-2y" "=" "-x-3
'........................................................................................................

color(green)("Step 2")

Change the equation so that the y term is positive

Multiply both sides by color(blue)(-1) giving:

" "+2y=+x+3" "->" "2y=x+3
'...............................................................................................
color(green)("Step 3")

Isolate y so that it is on the left of = and everything else is on the right.

Divide both sides by color(blue)(2)

" "color(brown)(2/(color(blue)(2)) xxy=x/(color(blue)(2))+3/(color(blue)(2))

But 2/2=1" and "1xxy=y

" "=>y=x/2+3/2..............................Equation (1)
'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
color(red)("Building the new equation")

Standard form is y=mx+c" whare m is the gradient (slope)"

From equation (1) the gradient is 1/2

We are given that the new line passes through the point:
" "P->(x,y)=(-1,2)

'.....................................................................................................
Substituting into equation (1)

color(brown)(y=mx+c)color(blue)(" "->" "2=1/2(-1)+c)

" "2=-1/2+c

Add 1/2 to both sides

" "2 1/2=c

Thus the new equation is:

" "color(magenta)(y=1/2x+2 1/2)