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How to find the y-intercept from this equation

y = 1 - (x - 2)^2

I understand that to get the y intercept, you have to set x = 0?

So y = 1 - (0 - 2)^2

therefore, y = 1 +/- 4 (not really sure which one? should it be positive or negative?)

y = 5 or y = -3

both are wrong tho for some reason? the answer is actually that the y-intercept is -5.

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Reply 1
Avatar for B_9710
B_9710
18
(−2)2=4 (-2)^2 = 4 .
So y=1−(−2)2=1−4=−3 y=1-(-2)^2=1-4=-3 . There can be no other answer.
Reply 2
Avatar for Zacken
Zacken
22
Original post by frostyy
y = 1 - (x - 2)^2

I understand that to get the y intercept, you have to set x = 0?

So y = 1 - (0 - 2)^2

therefore, y = 1 +/- 4 (not really sure which one? should it be positive or negative?)

y = 5 or y = -3

both are wrong tho for some reason? the answer is actually that the y-intercept is -5.


(0−2)2=(−2)2=−2×−2=4(0-2)^2 = (-2)^2 = -2 \times -2 = 4

So 1−(−2)2=1−4=−31 - (-2)^2 = 1- 4 = -3
Reply 3
Avatar for frostyy
frostyy
OP
17
Original post by Zacken
(0−2)2=(−2)2=−2×−2=4(0-2)^2 = (-2)^2 = -2 \times -2 = 4

So 1−(−2)2=1−4=−31 - (-2)^2 = 1- 4 = -3


why is the y-intercept equal to -5 then? I swear that y-intercept is when x = 0?
Reply 4
Avatar for Zacken
Zacken
22
Original post by frostyy
why is the y-intercept equal to -5 then? I swear that y-intercept is when x = 0?


It's not. Where does it say that it is? :redface:
Reply 5
Avatar for Notnek
Notnek
21
Original post by frostyy
why is the y-intercept equal to -5 then?

It isn't.

Two people have shown you that the y-intercept is -3.
Original post by frostyy
y = 1 - (x - 2)^2

I understand that to get the y intercept, you have to set x = 0?

So y = 1 - (0 - 2)^2

therefore, y = 1 +/- 4 (not really sure which one? should it be positive or negative?)

y = 5 or y = -3

both are wrong tho for some reason? the answer is actually that the y-intercept is -5.


Squaring a number always produces a positive so its 1 - (positive number)
Reply 7
Avatar for frostyy
frostyy
OP
17
Original post by Zacken
It's not. Where does it say that it is? :redface:

Nevermind, I made a mistake whilst completing the square ^^
Sorry for bothering you.
Reply 8
Avatar for Zacken
Zacken
22
Original post by Xenon17
Squaring a number always produces a positive so its 1 - (positive number)


Pedantry: 02=00^2 = 0. :tongue:
Reply 9
Avatar for Zacken
Zacken
22
Original post by frostyy
Nevermind, I made a mistake whilst completing the square ^^
Sorry for bothering you.


It's not a bother, don't worry. :h:
Original post by Zacken
Pedantry: 02=00^2 = 0. :tongue:


okay squaring a number never produces a negative.
Reply 11
Avatar for B_9710
B_9710
18
Original post by Xenon17
Squaring a number* always produces a positive so its 1 - (positive number)


*Real* number :wink:
Reply 12
Avatar for Zacken
Zacken
22
Original post by Ishan_2000
OP has said that the answer is actually -5.

However, this can't be right, if the equation of the line is y = 1 - (x - 2)^2


Yeah, that's been established. Also, it's a curve, not a line. :tongue:

If you sub in y= -5, then x = (square root of 6) + 2, which isn't 0, so -5 cannot be the y-intercept.


Or the simple observation that −3≠−5-3 \neq -5 suffices.

(How do you use LaText on this? :biggrin:)


The LaTeX\LaTeX guide is here.
Reply 13
Avatar for Zacken
Zacken
22
Original post by Xenon17
okay squaring a number never produces a negative.


Yep! In mathematical terms, we say: squares are non-negative. :smile:
Original post by B_9710
*Real* number :wink:


Okay calm down no need to get your knickers in a twist.
Original post by Zacken
Yep! In mathematical terms, we say: squares are non-negative. :smile:


I prefer thug life terms sorry
Reply 16
Avatar for Zacken
Zacken
22
Original post by Xenon17
I prefer thug life terms sorry


It's the maths forum not the thug life forum sorry
Wouldn't really call something that basic 'Mathematical terms'
Original post by Zacken
It's the maths forum not the thug life forum sorry


the thug life is universal
Reply 19
Avatar for Zacken
Zacken
22
Original post by Foxab77
Wouldn't really call something that basic 'Mathematical terms'


Uh... I don't see why being basic means that it's not a mathematical term... is 'addition' so basic that you'd say it's not a mathematical term?

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