Question

Choose the equation that represents a line that passes through points (−1, 2) and (3, 1). A)4x − y = −6 B)x + 4y = 7 C)x − 4y = −9 D)4x + y = 2

Answer 1

Answer:

B.

Step-by-step explanation:

I think I'm going to go with the plug in method here.

If you get the same value on both sides, then the point is contained on the line.

A)

4x-y=-6

Test (-1,2):  4(-1)-2=-6

4(-1)-2=-6

-4-2=-6

-6=-6

True; the equation holds for (-1,2).

Test (3,1): 4(3)-1=-6

4(3)-1=-6

12-1=-6

11=-6

False; the equation doesn't hold for (3,1).

A isn't the right choice.

B)

x+4y=7

Test (-1,2): -1+4(2)=7

-1+4(2)=7

-1+8=7

7=7

True, the equation holds for (-1,2).

Test (3,1): 3+4(1)=7

3+4(1)=7

3+4=7

7=7

True, the equation holds for (3,1).

Since the equation held for both (-1,2) and (3,1) then B is the right answer.

-------------------Let's also go ahead and find the equation another way:

(3,1) and (1,-2) are points on your line.

I'm going to write an equation for these points in slope-intercept form first which is y=mx+b where m is slope and b is y-intercept.

I will then rearrange into standard form like your choices are in.

m=slope=rise/run.

To find this, I like to line up the points and subtract and then put 2nd difference over 1st difference.

Like so:

(-1,2)

-(3,1)

---------

-4    1

The slope is 1/-4 or -1/4.

So the equation so far is y=-1/4 x+b since m=-1/4.

Now to find b, I'm going to use y=-1/4 x +b along with one of the given points on the line like (x,y)=(-1,2).

y=-1/4 x+b

2=-1/4 (-1)+b

2=1/4+b

Subtract 1/4 on both sides:

2-1/4=b

7/4=b

So the equation of the line is y=-1/4 x +7/4.

Now the goal is to write in ax+by=c form where a,b,c are integers.

Multiply both sides of y= -1/4 x +7/4 by 4 giving you:

4y=-1x+7

Add 1x on both sides:

1x+4y=7

or

x+4y=7 since 1x=x

So x+4y=7 is the answer if you prefer this way. Well anyway you prefer, this is the correct standard form for this line.

Answer 2

Answer:

B. x + 4y = 7

Step-by-step explanation: