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Write the equations of the lines, representing the following conditions, in the form y = mx + b, where m is the slope and b is the y-intercept: Part A: Passes through (4, 3) and m = start fraction two over five end fraction Part B: Passes through (−4, 2) and (2, −5) Part C: m = start fraction three over five end fraction and y-intercept = −4 Part D: x-Intercept = 7 and y-intercept = −2 Part E: Passes through (−2, 2) and parallel to 4x − 3y − 7 = 0

 Jul 17, 2016
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Slope-intercept form of a straight line:  y  =  mx + b

Point-slope form of a straight line:        y - y1  =  m(x - x1)

 

A)  Through  (4,3 ) and  m  =  2/5

      --->  Use the point-slope form with  m = 2/5,  x1 = 4, and  y = 3:     y - 3  =  (2/5)(x - 4)

              --->   Cross-multiply:  5(y - 3)  =  2(x - 4)   --->   5y - 15  =  2x - 8   --->   5y  =  2x + 7    --->   y  =  (2/5)x + (7/5)

 

B)  Through  (-4,2)  and  (2,-5)

     --->  First:  find the slope:  m  =  (-5 - 2) / (2 - -4)  =  -7/6

     --->   Use the point-slope form (using either point):  y - 2  =  (-7/6)(x - -4)

     --->     6(y - 2)  =  -7(x + 4)   --->   6y - 12  =  -7x - 28   --->   6y  =  -7x - 16   --->   y  =  (-7/6)x - 8/ 3

 

C)  m = 3/5  and  y-intercept -4:

     --->  Use the slope-intercept form:  y  =  (3/5)x - 4

 

D)  x-int = 7  and  y-int = -2:

     --->  x-int = 7   --->   (7,0)

             y-int = -2   --->   (0,-2)

     --->  First:  find the slope:  m  =  (-2 - 0) / (0 - 7)  =  -2/-7  =  2/7

     --->   Use the slope-intercept form:  y  =  (2/7)x - 2

 

E)  Passes through  (-2,2)  and is parallel to  4x - 3y -7  =  0:

     --->   All parallel lines have the same x-coefficient and the same y-coefficient; so, all lines parallel to 4x - 3y -7  =  0                 have the form:  4x - 3y + k  =  0  (for some value of k).

     --->   To find the value of  k  replace x with -2  and  y with 2:

              --->     4(-2) - 3(2) + k  =  0   --->   -8 - 6 + k  =  0   --->   -14 + k  =  0   --->   k = 14

              --->  Equation:  4x - 3y - 14  =  0

 Jul 17, 2016

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