Slope intercept form questions?

Slope-intercept form question?

• I have to write the equation of each line in slope-intercept form. I know slope intercept is y=mx+b.. i think i have the answers but heres the questions! A) m= 2/5, (2,1) B) m= -1/3, (6,3) C) m= 4, (0,7) D) m= -2, (4,-12) Here are the answers I got: A) 1=2/5 (2) + b B) 3= -1/3 (6) + b C) 4= 4/1 (0) + b D) -12= -2/1 (4) + b Thanks for taking the time to look over this! I think I have them right.. I'm just not sure. If I did get one wrong please correct it and show me how you got them. Thanks!

• Answer:

  Well, I think you are on the right track as far as understanding where slope fits in the equation. But you are supposed to figure out what b is for each of them (b is the y-intercept). You can't leave your answers with that ' +b '. You're not quite seeing how the point-slope form works. You can't just plug in the x and y values of a point like you are doing. (That's why you are not finding b.) I'll do the first two to show you how to find b. It's the same procedure for the other two. In all of these, you are given the slope and a point. So what you are trying to do really is convert from point-slope form to slope-intercept form. The point-slope form of an equation of a line is (y - y1) = m(x - x1). ------------ A. m = (2/5) , the point given is (x1,y1) = (2,1) Put those values into the point-slope form and solve for y : (y - y1) = m(x - x1) (y - 1) = (2/5)(x - 2) y - 1 = (2/5)x - (4/5) . . . . . . . . . [ multiplied out the right-hand side ] y = (2/5)x - (4/5) + 1 . . . . . . . . . [ added 1 to both sides ] y = (2/5)x + (1/5) . . . . . . . . . . . <---- that's the slope-intercept equation of the line ----------------- B. m= -1/3, (6,3) (y - y1) = m(x - x1) (y - 3) = (-1/3)(x - 6) y - 3 = (-1/3)x + (-1/3)(-6) y - 3 = (-1/3)x + 2 y = (-1/3)x + 2 + 3 . . . . . . . . . . [ added 3 to both sides ] y = (-1/3)x + 5 . . . . . . . . . . . . . <---- that's the slope-intercept form