00:01
All right.
00:03
Question 74.
00:06
Question 74 is a four equation for variable system.
00:12
So we're going to have to do some substituting.
00:17
So when i look at equation number one, i see that it doesn't have a b variable, but i also know that a has a coefficient of one.
00:26
So i'm going to solve equation number one for a.
00:32
So when i do that, i have to subtract c and subtract 2d from both sides.
00:41
So a equals negative 4 minus c minus 2d.
00:49
When i look at equation number two, i notice that the leading coefficient b also has a 1.
00:59
So it's coefficient of 1.
01:01
So i'm going to solve equation number 2 or b or letter b.
01:09
And in order to do that, i have to add 2c to both sides.
01:13
So b equals 1 plus 2c.
01:19
The next thing i'm going to do is go to equation number 3.
01:24
And i'm going to sub in the values of a and b.
01:31
From what i just wrote for equations 1 and 2.
01:36
So equation number 3, a, which is negative 4 minus c minus 2d, plus 2b plus 2 times 1 plus 2c minus c equals negative 2.
01:59
So i'm going to distribute right here and simplify kind of all at the same time.
02:08
So negative 4 minus c minus 2d plus 2 times 1 is 2, plus 2 times 2c is 4c minus c equals negative 2.
02:26
Okay.
02:27
So negative 4 and negative 2 equal negative 2.
02:35
So i have negative 2 on both sides.
02:38
Goes away.
02:40
Negative c, negative c, and a positive 4c equal 2c.
02:47
So 2c minus 2d equals 0.
02:52
I'm going to add 2d to both sides.
02:55
So 2c equals 2d, which means that c, c, i divide both sides by two, equals d.
03:03
Okay, so that's amazing.
03:06
Let's open up a new screen.
03:09
So c equals d.
03:13
All right.
03:14
So the next thing that i'm going to do is i'm going to rewrite equation number one, a plus c plus 2d equals.
03:38
Negative 4...