writing equations in slope intercept form and standard form

Question

write the equation of the line passing through [1,2] and [-2,5] in slope intercept form and standard form

Answer 1

The required line has a slope of -1. Hence, the equation will be y=-x+C. To find C we plug in the values x=1 and y=2 to obtain that C=3. So the equation is y=-x+3 or x+y=3.