Question

Write the equation of the line that has the slope m=2/5 and passes through the point ​(25​,−9​). Write the equation in​ slope-intercept form if possible.
I thought y=2/5x-9 but that's not right?

Answer 1

You're given the slope of the line and a point thru which the line passes.  So it makes sense to use the point-slope form of the equation of a straight line:  if the point is (a,b) and the slope is m, then 

y-b=m(x-a).  You'd then solve this for y to obtain the equation in slope-intercept form.

On the other hand, if you're asked to write the equation in slope-intercept form, starting with the general form of this equation may be faster:  y=mx+b.

Substitute the given values for x and y (which are 25 and -9) and m (which is (2/5).  Solve the resulting equation for b (the y-intercept).

Then write the finished equation:  y=( ? )x + b, where b is the y-intercept you've just found.