# Making an equation.

• Feb 17th 2008, 11:21 AM
LisaAnn_86
Making an equation.
Find the equation for each of the followings items below:
a. A line that passes through (1, 1) and is perpendicular to the line 3x+4Y=12.
b. A line that passes through (5,4) and has a slope of 2.
c. A line that passes through (9,8) and has a slope of -1.
d. A line that passes though the points (1,2) and (12,24)
e. A circle with a radius of 9 and a midpoint at (3,3)

How would I even begin. I'm lost. Hope you can help.Cheers.
• Feb 17th 2008, 11:35 AM
mr fantastic
Quote:

Originally Posted by LisaAnn_86
Find the equation for each of the followings items below:
a. A line that passes through (1, 1) and is perpendicular to the line 3x+4Y=12.
b. A line that passes through (5,4) and has a slope of 2.
c. A line that passes through (9,8) and has a slope of -1.
d. A line that passes though the points (1,2) and (12,24)
e. A circle with a radius of 9 and a midpoint at (3,3)

How would I even begin. I'm lost. Hope you can help.Cheers.

For a. - d., you need to find two things: the gradient and a point on the line. Get those two things and substitute into $y - y_1 = m(x - x_1)$ where m is the gradient and $\, (x_1, \, y_1)\,$ is a point on the line.

You're lucky that in each case, a point on the line is given to you. So you really only have to worry about finding m (and in c. even that is given to you) .....

For e., substitute the value for radius and the coordinates of centre (is that what you mean by midpoint?) into the standard equation for a circle. This equation has been stated in a reply to previous question.