We’re asked to

solve the equation 2x squared plus

3 is equal to 75. So in this situation,

it looks like we might be able to isolate

the x squared pretty simply. Because there’s only one

term that involves an x here. It’s only this x squared term. So let’s try to do that. So let me just rewrite it. We have 2x squared

plus 3 is equal to 75. And we’re going to try to

isolate this x squared over here. And the best way to do that,

or at least the first step, would be to subtract 3 from

both sides of this equation. So let’s subtract

3 from both sides. The left hand side, we’re

just left with 2x squared. That was the whole point of

subtracting 3 from both sides. And on the right hand

side, 75 minus 3 is 72. Now, I want to isolate

this x squared. I have a 2x squared here. So I could have just

an x squared here if I divide this side or

really both sides by 2. Anything I do to one side, I

have to do to the other side if I want to maintain

the equality. So the left side, just

becomes x squared. And the right hand side

is 72 divided by 2 is 36. So we’re left with x

squared is equal to 36. And then to solve for x,

we can take the positive, the plus or minus square

root of both sides. So we could say the plus or–

let me write it this way– If we take the square

root of both sides, we would get x is equal to

the plus or minus square root of 36, which is equal

to plus or minus 6. Let me just write

that on another line. So x is equal to

plus or minus 6. And remember here, if something

squared is equal to 36, that something could

be the negative version or the positive version. It could be the

principal root or it could be the negative root. Both negative 6 squared is

36 and positive 6 squared is 36, so both of these work. And you could put them back

into the original equation to verify it. Let’s do that. If you say 2 times

6 squared plus 3, that’s 2 times 36, which

is 72 plus 3 is 75. So that works. If you put negative

6 in there, you’re going to get the

exact same result. Because negative 6

squared is also 36. 2 times 36 is 72 plus 3 is 75.

my sister just told me everything this guy said within 5 seconds.

ORRLY?

best thing about Khan: he treats basic addition the same way he will treat the big bang theory explanation! xDD

Thank you so much, this really did help.

Thank lord these videos exist, my teacher can't teach for shit DX

Thank God

are u sure abt the ± because anything ^2 Is always positive ex -4*-4=+16

Wish I found this video before ripping my textbook in half out of frustration

nice

thank you sooo much my math's teacher is so bad she actually told me to check you out and now you are my teacher basically

OMG Thank you so much. When i was in 8th grade i used to hate watching these but now i appreciate them so much.

could you solve 9r2-3=-152