First we use sin(a+b)= sinacosb+sinbcosa
and cos(a+b)=cosa cosb -sinasinb
tan(x+pi/2)= sin(x+pi/2) / cos(x+pi/2)
and sin(x+pi/2) = sinxcospi/2 + sinpi/2cosx =cosx,
<span>cos(x+pi/2) = cosxcospi/2- sinxsinpi/2= - sinx,
</span> because <span>cospi/2 =0, </span>and <span>sinpi/2=1
</span><span>=tan(x+pi/2)= sin(x+pi/2) / cos(x+pi/2)= cosx / -sinx = -1/tanx = -cotx
</span>from where <span>tan(x+pi/2)=-cotx</span>
//To have the lines parallel, the gradients must be the same.
y -- 6 = 1/2 (x - 9)
y + 6 = 1/2 x -9/2
y = 1/2 x - 10.5
Okay to the first number in the ordered pair is the x and the second is the y. So (x,y) when you put a dot on the coordinate plane such as (2,3), you have to go the the horizontal line which is x and go over right 2 spaces(depending on how many numbers is one space) then go up 3. Do that same thing for each of the order pairs. Eventually you will have 4 dots. Connect those dots then you will have the quadrilateral. I hope this helps you!
