Mathswatch

Please could u help with part b) to a question. It says explain why x^2 -8x + 20 is always postive.

Its hard to get marks on mathswtach because the explaination has to be exact. If u could help that would be really appreciated. Thanks so much . Ive attached an image of the question .

OP

(edited 4 years ago)

okay well if you rearrange to complete the square, you get (x^2-4)^2 +4
and seeing as anything squared will always be positive or zero, the lowest possible value for (x^2-4)^2 is 0, when x = 4
and 0 + 4 = 4, which is greater than 0, so positive

hope that helps!

Reply 3

Pleasehelpme562

OP

2

Original post by dysf(x)al13

okay well if you rearrange to complete the square, you get (x^2-4)^2 +4
and seeing as anything squared will always be positive or zero, the lowest possible value for (x^2-4)^2 is 0, when x = 4
and 0 + 4 = 4, which is greater than 0, so positive

hope that helps!

I understand but is there any way of re wording this because mathswatch is marking it as wrong

Reply 4

Notnek

21

Original post by Pleasehelpme562

Did you mean to say, “add 2 to it”? The expression contains a 4 not a 2.

Reply 5

Pleasehelpme562

OP

2

Original post by Sir Cumference

Did you mean to say, “add 2 to it”? The expression contains a 4 not a 2.

I tried 4 at first but it was marked as wring so i wrote 2

Reply 6

Notnek

21

Original post by Pleasehelpme562

I tried 4 at first but it was marked as wring so i wrote 2

Well it's clear that you understand the concept and would get marks in a real exam but unfortunately Mathswatch isn't clever enough to replace a teacher/examiner. I recommend that you keep trying different wording to explain the same thing until it accepts it. @Muttley79 may have some suggestions?

Reply 7

Muttley79

20

Original post by Pleasehelpme562

I tried 4 at first but it was marked as wring so i wrote 2

Mathswatch is incredibly annoying and we don't use it because it is very pedantic -

Try different things (x - 4)^2 is always great than or equal to zero

So (x - 4)^2 + 4 > 0 for all values of x.

Good luck in funding the key words the programme is looking for!

Reply 8

Yasminfnaf

3

I'm afraid the HENCE in part b) suggests you should use your answer from part a).
Replacing 'anything squared' from your answer with '(x-4)^2' would probably give you the mark.

Reply 9

Dt00000

1

Original post by Yasminfnaf

I'm afraid the HENCE in part b) suggests you should use your answer from part a).
Replacing 'anything squared' from your answer with '(x-4)^2' would probably give you the mark.

This marked it correct thank you

Reply 10

hahmed191

1

Original post by Yasminfnaf

I'm afraid the HENCE in part b) suggests you should use your answer from part a).
Replacing 'anything squared' from your answer with '(x-4)^2' would probably give you the mark.

thanku

Reply 11

Helpneedspls

Original post by Pleasehelpme562

I tried 4 at first but it was marked as wring so i wrote 2

If you write “ (x-4)² is always positive or equal to zero, and if you add 4 to it, it must be above zero so x²-8x+20 is positive”

I got full marks when u wrote this, but i had to copy and paste the squared from a different question becuase it didnt give me the squared option

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