# Help with equations of lines.

• Mar 13th 2011, 11:34 AM
ineedhelplol
Help with equations of lines.
can someone answers these please? These are the ones i got wrong on a test and i ant to know the write answers so i can do better

1. Write an equation for the line that has slope 5/3 and intersects the y-axis at -6

2. A hang glider takes off from an 800-ft cliff. After 5 minutes he is at an altitude of 500 ft.

A. Determine the rate of change

B. Write a linear equation to model the situation

3. Rewrite -3x+6y=12 in slope intercept form

4. Write an equation in point-slope form of the line passing through (-2,6) with slope -5/7

5, The line perpindiuclar to y=-3x-1 has a slope of....

6. Write an equation of the line parrallel to y=-1/2x+9
• Mar 13th 2011, 12:03 PM
HallsofIvy
Quote:

Originally Posted by ineedhelplol
can someone answers these please? These are the ones i got wrong on a test and i ant to know the write answers so i can do better

1. Write an equation for the line that has slope 5/3 and intersects the y-axis at -6

A line with slope m can be written in the form y= mx+ b. And, of course, the line crosses the y-axis when x= 0 so y= m(0)+ b= b.

Quote:

2. A hang glider takes off from an 800-ft cliff. After 5 minutes he is at an altitude of 500 ft.

A. Determine the rate of change
So he went from 800 to 500. How many feet did he go up (be careful of the sign). And he did that in 5 minutes. How many feet per minute is that?

Quote:

B. Write a linear equation to model the situation
Again, y= mx+ b (x is the time in minutes here). You got the slope, m, in (A) and when x= 0 y= 800.

Quote:

3. Rewrite -3x+6y=12 in slope intercept form
"Slope intercept form" is "y= mx+ b". Solve for y.

Quote:

4. Write an equation in point-slope form of the line passing through (-2,6) with slope -5/7
Again, y= mx+ b.

Quote:

5, The line perpindiuclar to y=-3x-1 has a slope of....
If m1 and m2 are the slopes of two perpendicular lines, then m1m2= -1.

Quote:

6. Write an equation of the line parrallel to y=-1/2x+9
Surely the problem did not say "the" line. There are an infinite number of lines parallel to this or any line. Two lines are parallel if and only if they have the same slope.
• Mar 13th 2011, 12:07 PM
ineedhelplol
Can you answer them for me please? And yes my bad it didnt say the line.
• Mar 13th 2011, 12:32 PM
skeeter
Quote:

Originally Posted by ineedhelplol
i just need to know the answers

Sorry, but that it not how it works here at MHF ... Halls of Ivy has provided you the necessary guidance to find the solutions yourself. Post your work and solutions to get further guidance if necessary.
• Mar 13th 2011, 01:14 PM
ineedhelplol
1. y=5/3x-6

2. A. 300/50=60/1

B. ?

3. y=-1/2x+2

4. y-2=-5/7(x+6)

5. 1/3

6.y=-1/2x=8

are these right?
• Mar 13th 2011, 02:25 PM
mr fantastic
Quote:

Originally Posted by ineedhelplol
1. y=5/3x-6 Mr F says: Yes.

2. A. 300/50=60/1 Mr F says: Wrong sign.
B. ? Mr F says: Review the help you were given. What have you tried? Where are you stuck?

3. y=-1/2x+2 Mr F says: No. Do it more carefully.

4. y-2=-5/7(x+6) Mr F says: No. Does it pass through (-2, 6)? Go back and use the slope-point formula more carefully.

5. 1/3 Mr F says: Yes.

6.y=-1/2x=8 Mr F says: Yes.

are these right?

Most of your errors are careless mistakes.
• Mar 13th 2011, 03:11 PM
ineedhelplol
2. A. -60/1
B. 800=-60x-500?

3. ?

4. y-6=-5/7(x-(-2)
• Mar 13th 2011, 04:14 PM
mr fantastic
Quote:

Originally Posted by ineedhelplol
2. A. -60/1 Mr F says: Yes.
B. 800=-60x-500? Mr F says: This is not the equation of a line. Go back and read the help you were given.

3. ? Mr F says: See previous feedback.

4. y-6=-5/7(x-(-2) Mr F says: Yes. But another bracket is need at the end. And yuor teacher may want it in y = mx + c form.

..
• Mar 13th 2011, 04:17 PM
ineedhelplol
y = -300/800x + 0

is that the answer to 2b?
• Mar 13th 2011, 04:23 PM
mr fantastic
Quote:

Originally Posted by ineedhelplol
y = -300/800x + 0

is that the answer to 2b?

For goodness sake! Stop guessing and read what you were told in post #2.
• Mar 13th 2011, 04:28 PM
ineedhelplol
800=-60/1x+0

thats gotta be it.
• Mar 13th 2011, 06:09 PM
mr fantastic
Quote:

Originally Posted by ineedhelplol
800=-60/1x+0

thats gotta be it.

That's NOT an equation that relates height to time.

You have already shown some understanding of using the slope-point form y - y1 = m(x - x1). I do not know why you can't correctly apply it here.