@joymariearga

its just amazing how this video is uploaded way back in 2010 but is still very useful today and will be for the years to come. Thank you Khan Academy!!

@KosovaWarrior

Teachers in our school just complicate it as much as possible to mash our brains...but you Khan Academy are something that brought help to me and many other people...I am making progress in math only because of you and not because of my teachers...they are very bad,thank you,keep going.

@shreendawg123

why cant my schools just play your vids in classes???

@TasyaAdzkiya

5:15 Additional notes from me: a variable is a "bucket" that can be any number based on its constraints and can be changed to any symbol, letter, or maybe shapes (it's basically anything distinct to be used to represent the "bucket") without changing the value of the expression.

Up until x = f inverse of y = (1/2)y - 2, y is useful to see where it's coming from: it's coming from the original equation y = f(x) = 2x + 4, we just solve for x in terms of y to map from the range back to the domain or to make the output as the input and vice versa (that is why it is called inverse function). 

After we know where it's coming from, it's useful that at this point and onward, we change the symbol/variable from y to x to see the relationship between f inverse of y to f(x) or f of x. We can do that because we just change the symbol or the variable without changing the value. We could've change the y into a or b or anything, but we chose to change the y into x because we need to see the relationship between the f inverse of y and the f(x) or f of x.

• x = f inverse of y = (1/2)y - 2 --------> change the letter y to X to see the correlation between this equation to f(x) (it's not going to change the value, it's the same as if you were to use star shapes to represent a variable and decide to change them to heart shapes)
• x = f inverse of X = (1/2)X -2

We now see the correlation between f inverse of X and f(x) or f of x. In fact, f inverse of X is derived from f(x).

Notice that it might be a little confusing since now, in the x or f inverse of X equation, the domain (input) and range (output) are represented by the same variable, they are just differentiated by means of capital letter and lowercase letter: x = f inverse of X (let us use capital X as the input and the lowercase x as the output to differentiate them) = (1/2)X - 2.

• The x (range or output) = f inverse of X (domain or input) is similar to the y (range or output) in y (range or output) = f(x) or f of x (domain or input).
• The X (domain or input) in x (range or output) = f inverse of X (domain or input) is similar to the x (domain or input) in y (range or output) = f(x) or f of x (domain or input).

@vmartin222

THANK YOU KAHN ACADEMY YOURE  MY HERO IF I GAVE YOU A DOLLAR FOR EVERY TIME YOU HAVE MADE EVERYTHING CLEAR I WOULD BE IN REALLY BAD DEBT

@yonu2953

Nice watching this 10 years later cause of corona🦠

@kennywells9328

Got nothing but praise for this guy. He actually makes sense teaching math.

@MICHAELSMITH-eb4br

This video was super helpful. Your ability to explain things makes it unbelievably easy to comprehend and conceptualize these otherwise confusing concepts. It's bizarre that I could spend about an hour in a class with an instructor going over this material and still left not knowing much more than I did at the beginning of that hour, yet I watch this video that's less than 10 minutes, and I totally get it now. However, what I can't wrap my brain around is how 69 individuals found this video unhelpful and gave it a thumbs down.

@stevenjames5874

Jussst when I thought I had almost all of the basic algebra down. I'm halfway through differential calculus and realized I needed to re learn this :)

@EatShanklish

I see you've updated your sketch pad. Never thought these videos could get any better than they already were. Thanks, Sal, your a lifesaver.

@khanacademy

@chizzy555 Maybe some trades.  I could imagine the inverse trig functions would be pretty useful if you're building something.

@snnacho

loving the new writing Sal. Much neater!

@Peacefulcrystalmoon

you explain better than my math teacher ever could in his life! THANK YOU! My head does not swim in confusion anymore thanks to your detailed lessons!

@nyssia7

Crazy how this video was made before I turned 5 and now I'm watching it as a freshman in college

@cboyslim5490

khan academy is an Easy Mode feature for high school and college math lol

@LucasKVogt

THANKS SO MUCH I ALWAYS COME TO YALL WHEN I NEED MATH HELP YOU'RE THE BEST!!!!

@mercilesscuttlefish

i would never have made it through half of last year without these videos. thanks so much man.

@yashaswikulshreshtha1588

Dude, like literally YOU'RE THE BEST. Your videos are so intuitive. I love it, I have been after teachers to tell me what's inverse they would tell  me it's opposite of what it does, I knew what they wanna say but i felt unsatisfied like it didn't make sense although I knew how to do it. But that part where you just told that question is there any way to get back to the x. After that why you solved for x made perfect sense....

@pforrest10

i had a moment when i had to pause the video just to be like "ohhhhhhhhh" cuz I finally understood. learning over zoom has been terrible but this was so helpful

@adithyareddy3766

Simplifying things so much.has been a great help to understand concept easily.thnk u