Geometry Stumper

[Albert Chan]

(08-15-2018 01:16 PM)Voldemar Wrote:  

(08-15-2018 12:29 PM)Albert Chan Wrote:  BTW, have you peek at Thomas Puettmann sketch, about the green lines ?
Why is that a right triangle ?

There are 4 angles at C. Two angles x and two angles y.
2x + 2y = 180
Divide by 2
x + y = 180/2 = 90
Angle x + y is our angle in the green lines.

this is enough to prove the whole thing !

the other side will have two angle y and two angle z, y + z = 90

--> angle DCE = x + y + y + z = (x+y) + (y+z) = 90 + 90 = 180

Wow, the power of geometry.