That's correct, you can. It is completely irrelevant to what I was talking about, but yes, granted, not all intersecting lines in the universe have to have right angles. Well done Little Jimmy, have a cookie.
Now back onto what I ACTUALLY said...
"You do realise that
if you have two straight lines that cross over each other, where ONE of the four angles between the two lines is a right angle, then ALL THE OTHER THREE of the four angles will also be right angles*."
How do we know this? Well, we can use the devil's angle measuring instrument, the protractor to prove it.
Take any two intersecting lines, and the four angles made between the two lines add up to 360 degrees:
In mathematical terms, a + b + c + d = 360 degrees regardless of how you draw those two lines.
You can measure it to prove it, but really it's just common sense. Everyone knows that "360 degrees" means "all the way back around to where you started".
It also also be plainly obvious that a + b = 180 degrees. You can see it without needing to measure it, but if you need to, grab a protractor and try it yourself.
And therefore that c + d = 180 degrees.
And also that a + c = 180 degrees.
And also that b + d = 180 degrees.
Now, let's say that in a diagram similar to this one, we know that a = 100 degrees.
From there we can then work out what the angles b, c and d all are, just by pure logic.
if a + c = 180 degrees
and a = 100 degrees
then c = 180 degrees minus 100 degrees
therefore c = 80 degrees.
If you do that same simple equation two more times you'll see that in this example,
a = 100 degrees
b = 80 degrees
c = 80 degrees
d = 100 degrees
Now, let's do that again but for an example where a = 90 degrees (aka a "right angle").
If a + c = 180 degrees
and a = 90 degrees
then c = 180 degrees minus 90 degrees
therefore c = 90 degrees
if a + b = 180 degrees
and a = 90 degrees
then b = 180 degrees minus 90 degrees
therefore b = 90 degrees
We already now know the values of both b and c as well as the original angle a, so we can use any of three methods to get the final angle:
The first two methods are the same as the one we've just used repeatedly:
If c + b = 180 degrees
and c = 90 degrees
then d = 180 degrees minus 90 degrees
therefore d = 90 degrees
or
If b + d = 180 degrees
and b = 90 degrees
then d = 180 degrees minus 90 degrees
therefore d = 90 degrees
or method 3, going back to the original 360 degrees equation:
a + b + c + d = 360 degrees
therefore:
90 + 90 + 90 + d = 360 degrees
therefore:
d = 360 - (90 + 90 + 90) degrees
therefore
d = 360 - 270 degrees
therefore d = 90 degrees
No, again I was just protecting myself from you deflecting by saying something like "I've drawn my lines on the humps of a camel rather than on a piece of paper and the angles don't add up to 360 degrees like you say they should".
No, pretty sure I was right the first time.
No, it's because they're happy to pick up a protractor and measure it. It's not a big con, it's a measuring tool for mathematics, something you claimed to believe in twenty-five pages ago.
I f***ing give up.
Come back after you've done a year of senior school.
And tell your parents they should sue your junior school for incompetence.