IS THIS GRAPH RIGHT? (Taking into account domain )

Jane122

Hi check my graph please.

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Reply 1

Jane122

@SeanFM @Maths 123 @gdunne42

Reply 2

Kevin De Bruyne

Original post by Jane122

@SeanFM @Maths 123 @gdunne42

Almost, I would be persnickety and say that the graph is not defined for x>4 or x<0 so there should be no lines there.

Reply 3

the bear

the curve should begin at ( 2, 4 ) ... this means it will be higher than the end of the straight line, which ends at ( 2, 2 )

(edited 7 years ago)

Reply 4

Jane122

Original post by SeanFM

Almost, I would be persnickety and say that the graph is not defined for x>4 or x<0 so there should be no lines there.

I'm confused 😅

Reply 5

Kevin De Bruyne

Original post by Jane122

I'm confused 😅

Well, what is f(-1)? How about f(5)? The answer is that they are not defined by the function f(x) so there should not be any y values for x values outside of the specified range. Your graph suggests that f(-1) = -1 and f(5) = 4*5 - 25.

And as the bear said.. I hadn't noticed.. your line should finish below the curve, if you see his post you'll understand why.

Reply 6

Jane122

Original post by the bear

the curve should begin at ( 2, 4 ) ... this means it will be higher than the end of the straight line, which ends at ( 2, 2 )

Like this ?

Reply 7

Jane122

Original post by SeanFM

F(1) is -5 and f(5) is also -5

Reply 8

Kevin De Bruyne

Original post by Jane122

F(1) is -5 and f(5) is also -5

They are not. Y values for this f(x) only exist between x=0 and x = 4. -5 and 5 are outside of this range so they have no corresponding y values.

Reply 9

Jane122

Original post by SeanFM

They are not. Y values for this f(x) only exist between x=0 and x = 4. -5 and 5 are outside of this range so they have no corresponding y values.

So the graph should end at 4? How am I supposed to know that?

Reply 10

fatima359

I'm not the only one whose looking at the graph and thinking WTF? 😁😁😁 Am I??

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Reply 11

Kevin De Bruyne

Original post by Jane122

So the graph should end at 4? How am I supposed to know that?

From the definition of the function.

Reply 12

fatima359

I'm not the only one whose looking at this graph and thinking WTF am I?? 😁😁

Posted from TSR Mobile

Reply 13

Ua3142

Original post by Jane122

Hi check my graph please.

ahh flashbacks! burn it! BURN IT!!!111ERE

Reply 14

Jane122

Original post by SeanFM

From the definition of the function.

Ok I am really really stuck.. I don't know why the graph stops dead at 4? Like if you draw beyond but that are the values not less than 4 still?

Reply 15

BobBobson

Original post by Jane122

So the graph should end at 4? How am I supposed to know that?

Since there is no function defined for any x after 4 or before 0, so no graph can be plotted. Also the endpoint for 4x-x^2 should be coloured in since it's not a strict inequality

(edited 7 years ago)

Reply 16

Jane122

Original post by BobBobson

Since there is no function defined for any x after 4 or before 0, so no graph can be plotted. Also the endpoint for 4x-x^2 should be coloured in since it's not a strict inequality

But the 4x-x^2 graph is going through 4???

Reply 17

Kevin De Bruyne

Original post by Jane122

Ok I am really really stuck.. I don't know why the graph stops dead at 4? Like if you draw beyond but that are the values not less than 4 still?

If you were in a sweet factory and there was a sign that said 'red sweets go into box 1 and blue sweets go into box 2' then where would green sweets go? Who knows. Green is not red or blue, so who can say where it goes? No one can. The same way this function tells you where values between 0 and 4 go but not for anything outside those values.

Reply 18

Jane122

Original post by SeanFM

I see what you mean like where would 5,6,7 etc go. But the way I drew the graph makes it look like it passes through 4

Reply 19

BobBobson

Original post by Jane122

But the 4x-x^2 graph is going through 4???

4x-x^2 does go through 4 normally, however in your OP, you said the domain for it is 2<= x <= 4, so your x co-ordinates should stop dead at 4. Any number past 4 isn't in the domain of 4x-x^2, and thus shouldn't be plotted.