Question

Convert (-4,6) and (-9,6) to polar points

Answer 1

@Koikkara

Answer 2

@aravin.....hope u know this bttr than me...

http://facultypages.morris.umn.edu/~mcquarrb/teachingarchive/Precalculus/Lectures/PolarCoordinates.pdf

refer....

Answer 3

i did r=sqrtx^2+y^2 but it didn't work

Answer 4

What didn't work?

Answer 5

\[\sqrt{(x^2)+(y^2)}\]

Answer 6

Hey, @abc123! Just do it like the other one!

r = sqrt(x²+y²)=sqrt((-4)²+6²)

Maybe problem w. brackets ?

Answer 7

thats what i did. i got 2sqrt13 but it said i was wrong

Answer 8

Well, \(\sqrt{52}=\sqrt{4 \cdot 13}=\sqrt{4}\cdot\sqrt{13}=2\sqrt{13}\), so that is OK!

Answer 9

but it says i am wrong so i don't know what to do

Answer 10

What angle did you get? Could that be the problem?

Answer 11

arccos(-4/2sqrt13)

Answer 12

That is about 2.16 radians. That is also OK.
You just gave the right answer.

Maybe the error occured after you gave the conversion of the other point, (-9, 6)?

Answer 13

no its two seperate questions

Answer 14

@ZeHanz ...i applaud You for the Explanation....Keep it up...!

Answer 15

Well @abc123!, sometimes you are right and the book, teacher, or whatever computer program is wrong!
Don't bother with it anymore, and go on with what you were doing!

Answer 16

ok

Answer 17

i am also having probs with (13,6) and (20,2)

Answer 18

@Koikkara: thx for the support!

Answer 19

@abc123!
What r's have you found?

Answer 20

for (13,6) i have sqrt205 and for (20,2) i have 2sqrt101. i know they r right. just the angles r wrong

Answer 21

OK, let's look into that.

What values did you get?

Answer 22

arccos(13/sqrt205) and arccos(20/2sqrt101)

Answer 23

There could be a slight problem with the last one: type arccos(20/(2sqrt101)) to be sure 20 gets divided not only by 2, but also by sqrt101.

Answer 24

no i converted it to a decimal

Answer 25

and got .996686525?

Answer 26

.09966865.....

Answer 27

Right again.
Are doing some kind of online test, where you have to type in your answers?

Answer 28

its online hw not a test

Answer 29

Are you shown the "right" answers at any time?

Answer 30

after the session is closed which is tuesday at 10

Answer 31

And you have to give the answers in decimal format? How many decimals?

Answer 32

hold on

Answer 33

it wont let me put in arccos so i think it has to be a decimal

Answer 34

Could you try arctan? I.e. arctan(6/13) for the point (13,6)

Answer 35

it says that 'Can't take acos of 100.498756211209" for arccos(20/2sqrt101) but i got the angle for (13,6)

Answer 36

arccos worked for (13,6)

Answer 37

We've found it!

Answer 38

@abc123!
To Convert from Cartesian to Polar
When you know a point in Cartesian Coordinates (x,y) and want it in Polar Coordinates (r,θ) you solve a right triangle with two known sides.

Example: What is (12,5) in Polar Coordinates?



Use Pythagoras Theorem to find the long side (the hypotenuse):

r2 = 122 + 52
r = √ (122 + 52)
r = √ (144 + 25) = √ (169) = 13
Use the Tangent Function to find the angle:

tan( θ ) = 5 / 12
θ = tan-1 ( 5 / 12 ) = 22.6° (to one decimal)

What is tan-1 ? It is the Inverse Tangent Function.

Tangent takes an angle and gives you a ratio,
Inverse Tangent takes a ratio (like "5/12") and gives you an angle.
Answer: the point (12,5) is (13, 22.6°) in Polar Coordinates.



So to convert from Cartesian Coordinates (x,y) to Polar Coordinates (r,θ):

r = √ ( x2 + y2 )
θ = tan-1 ( y / x )

Answer 39

It's what I told you earlier about 20/2sqrt101. it should be: 20/(2sqrt101)

Answer 40

ok. let me try

Answer 41

@niksva: thanks for the help, but we've got a "technical" problem here, I'm afraid...

Answer 42

yup it worked. but now i can't get anything for (-9,6) and (-4,6)

Answer 43

i got 2sqrt13 for (-4,6) and 3sqrt13 for (-9,6). it says its wrong

Answer 44

The r's we can do w/o calculator:
sqrt(81+36)=sqrt(117)=3sqrt(13)
sqrt(16+36)=sqrt(52)=2sqrt(13)

Answer 45

yeah thats what i got

Answer 46

OK now the thetas:

arctan(6/(-9))=-.5880. Adding pi gives 2.5536
arctan(6/(-4))=-.9828. Adding pi gives 2.1588

Answer 47

how do i put that in without a decimal

Answer 48

arctan(6/(-9))+pi ?

Answer 49

Can you input a greek letter pi?

Answer 50

yeah i can and its wrong

Answer 51

No, it's right, but the stupid prog doesn't know...

Answer 52

ok whatever thanks for helping

Answer 53

YW!

Answer 54

try putting in parens
i got 2sqrt13 for (-4,6) try 2 sqrt(13)

for the angle
try acos(-4/sqrt(52))

Answer 55

ok