If two lines are parallel, it means that they will have the same gradient:
And remember, the equation of a line is y = mx +c
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So we know that the equation of the parallel line is:
y = -
x + c through point (7, 4)
All we need to do now is to work out what c is
Note: at point (7, 4) x = 7 , and y = 4.
So to work out c, we substitute in the values of x and y, and solve:
y = -
x + c
4 = -
* 7 + c
4 = -1.4 + c
5.4 = c
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Finally, we just put the value of c back into the original equation
y = -
x + 5.4
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Answer:
The equation of the a line parallel to y = -
x + 3 through point (7,4)
is: y = -
x + 5.4