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SAT Math 8.3 Algebra and Functions 204 Views


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SAT Math 8.3 Algebra and Functions

Language:
English Language

Transcript

00:02

Here’s your shmoop du jour, brought to you by the difference of two squares.

00:06

Sure, all squares have their differences…but we hope these two can work things out.

00:12

If 9x2 - y2 = 15 and 3x - y = 3, what does 3x + y equal?

00:23

The most important thing is to recognize that, in this

00:25

problem, 9x squared minus y squared is a difference of two squares…

00:33

…so “a squared minus b squared” can be factored into “a minus b times a plus b”.

00:41

9x squared is 3x times 3x.

00:43

So we can factor the first equation so it becomes (3x + y) times (3x - y) = 15.

00:50

Then we give a little whistle and call over the second equation…which we can now substitute:

00:55

(3x + y) times 3 = 15; then, dividing both sides by 3, we get 3x + y = 5.

01:01

So our correct answer is 5. Good boy. Now…roll over.

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