y = 1/2 x + 1

The line cd is parallel to the line Ab so the gradients are equaled:

SO for line cd we have y = 1/2 x + c.. now we substitute (1,4)

4 = 1/2(1)+c --> c= 7/2. --> y = 1/2 x + 7/2...

For line bc the line intersects at a right angle use this property to find the equation....