1
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Evaluate 3x^2-8x+7 when x=-2.

2
00:00:07,779 --> 00:00:11,000
So to evaluate this expression when x is equal to -2

3
00:00:11,000 --> 00:00:15,256
everywhere that we see an x we just have to substitute it with a -2.

4
00:00:15,256 --> 00:00:22,175
So it would be 3 times, instead of x^2, it would be -2^2 minus 8 times...

5
00:00:22,175 --> 00:00:27,237
instead of 8 times x, 8 times -2 plus seven.

6
00:00:27,237 --> 00:00:29,002
And so what does this give us?

7
00:00:29,002 --> 00:00:32,345
So we have 3 times -2^2.

8
00:00:32,345 --> 00:00:33,599
Well, that's just positive 4.

9
00:00:33,599 --> 00:00:36,067
Negative times a negative is a positive.

10
00:00:36,067 --> 00:00:40,844
Minus 8 times -2 is -16.

11
00:00:40,844 --> 00:00:43,909
-16 plus 7.

12
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So 3 times 4 is 12.

13
00:00:46,928 --> 00:00:49,993
You're sub... from that you're subtracting -16.

14
00:00:49,993 --> 00:00:53,661
Subtracting -16 is the same thing as adding positive 16.

15
00:00:53,661 --> 00:00:57,655
So, it's 12 plus 16 plus 7.

16
00:00:57,655 --> 00:01:01,649
And so this is equal to 12 plus 16 is 28.

17
00:01:01,649 --> 00:01:04,668
And if you add 7 to 28, you get...

18
00:01:04,668 --> 99:59:59,999
you get 35.