Point slope form:

m=slope
(x1,y1)
First we need to find the slope using the slope formula:

Given the two coordinates:
<span>(1, 9) and (−1, 11)
Plug them into the slope formula:
</span>

Simplify:

<span>
Now we know that:
m=-1 and the (x1,y1) would be </span><span>(1, 9)
</span>
Now we simply plug in the info:
Final answer: y − 9 = −(x − 1)
You have to prove that 2 angles are conguent to the other triangles angles; example: ∠A≅∠C by the additon POC (2 of those) and then one side; example: AB≅BA by the reflexive POE (1 of those)
I cant see the triangles but thats how you do them, also im learning this right now too, look up the triangle congruence things like ASA ≅ SSS≅ HL≅ exc. a chart will explain how to prove them using that:
Two planes intersect in a line sometimes.