00:01
We're given a right triangle with sides 2x, x plus 5, and 3x plus 1, and so we're asked to find the actual length of the side.
00:08
In order to do that, we need to find a value of x.
00:11
So we're going to use pythagrin theorem.
00:13
So a squared plus b squared is equal to c squared.
00:16
C is always across the right angle.
00:19
So this is c.
00:20
A and b.
00:22
It doesn't matter which is a or b.
00:24
So i'm going to have 2x squared plus x plus 5 squared is equal.
00:31
To 3x plus 1 squared.
00:35
So 2x squared is 4x squared.
00:38
X plus 5 squared is you use the square of a binomial, so you take the first term in squared, so that's x squared.
00:47
To get the second term, you multiply x and 5 and double it, so you get 10x.
00:52
To get the last term, you take a 5 and you square that, and that's a plus 25.
00:58
Do the same thing with the other side.
01:00
3x squared becomes 9x squared, we multiply the first term and the last term, so that's 3x.
01:08
Then you double it, so that's 6x.
01:11
Then we take the last term and we square it, and that becomes 1.
01:17
So we're going to combine like terms.
01:20
I have 5x squared plus 10x plus 25 is equal to 9x squared plus 6x plus 1.
01:29
I'm going to move everything from the left side to the right side so i can keep the x squared positive.
01:35
So i'm going to subtract x squared.
01:38
I'm going to subtract 10x and make sure you line it up with the common terms and subtract 25.
01:46
So this all goes to zero and you're left with 4x squared minus 4x minus 24.
01:55
Before i factor that, i notice all of these are divisible by four, so i'm going to divide the entire thing by four.
02:02
So i get 0 is equal to x squared minus x minus 6.
02:07
Makes it easier to factor.
02:10
So i know i'm going to have two parentheses equal to zero...