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# help watch

1. show that the straight line y=x +4 touches the circle with equation x^2 + y^2 = 13 at two points. find the cordinates of each point..

i keep on getting a different answer from what my book is telling me..

Zacken easy for you!

any help will be appreciated!
2. (Original post by manuel132)
show that the straight line y=x +4 touches the circle with equation x^2 + y^2 = 13 at two points. find the cordinates of each point..

i keep on getting a different answer from what my book is telling me..

Zacken easy for you!

any help will be appreciated!
Subsitute into the circle equation to get: , what do you get when you expand this out? What's your final answer?

I'm moving this to maths - by the way. :-)
3. (Original post by Zacken)
Subsitute into the circle equation to get: , what do you get when you expand this out? What's your final answer?

I'm moving this to maths - by the way. :-)
oh nooooooooo!! sorry.. it is y= 5x + 13 instead
4. x^2+(5x+13)^2=13 -> 26x^2+130x+156=0 -> x^2+5x+6=0, now solve.
5. Zacken i did (x+y)(x-y)= 13 and then i substituted y with 5x +13 .. can you tell me why i am wrong? thanks
6. (Original post by manuel132)
oh nooooooooo!! sorry.. it is y= 5x + 13 instead
Plug this into the circle equation to get: , can you expand this? What do you get when you expand it?
7. (Original post by manuel132)
Zacken i did (x+y)(x-y)= 13 and then i substituted y with 5x +13 .. can you tell me why i am wrong? thanks
8. (Original post by constellarknight)
x^2+(5x+13)^2=13 -> 26x^2+130x+156=0 -> x^2+5x+6=0, now solve.
i can do that but i wanted to approach it in a dfferent way..look at my last post and tell f i am wrong and if so, why
9. As Zacken said, (x+y)(x-y)=x^2-y^2, not x^2+y^2. If you wanted to factorise it would be (x+iy)(x-iy)=13, but that wouldn't really help you.
10. (Original post by Zacken)
damn haha thanks dude. so what if i did (x + y)(x+y) and substituted?
11. (Original post by manuel132)
damn haha thanks dude. so what if i did (x + y)(x+y) and substituted?
12. (Original post by Zacken)
i get it haha.. so how do i factorise x^2 + y^2?

i don't think i can
13. In general, most operations are not distributive (i.e. for almost all functions f, f(x+y) does not equal f(x)+f(y)).
14. (Original post by manuel132)
i get it haha.. so how do i factorise x^2 + y^2?
You can't factorise that over the real numbers, unfortunately. You'll need to do it the way I showed you.
15. (Original post by Zacken)
You can't factorise that over the real numbers, unfortunately. You'll need to do it the way I showed you.
diìo you mind if i pm you questions i don't get instead of making threads?
16. (Original post by constellarknight)
In general, most operations are not distributive (i.e. for almost all functions f, f(x+y) does not equal f(x)+f(y)).
thanks, do you mind if i pm you questions i don't understand?
17. (Original post by manuel132)
diìo you mind if i pm you questions i don't get instead of making threads?
I'd rather you make a thread - everybody can benefit from it then, is there a reason you prefer PM to thread?
18. (Original post by Zacken)
I'd rather you make a thread - everybody can benefit from it then, is there a reason you prefer PM to thread?
because i understand much more compared to making a thread and also, i won't be posting in the wrong forum haha

solve
at the start of the year, a traiin s half full. each week the number of people cathinng this increases by 1%
how many week will it be before the train is full?

and

how many times is 2.56 x 10^27 bigger than 5 x 10^5?

i do have the answers but i don't know how to begin solving the que.. i had 50 weeks for the first one but according to the book i am wrong
19. (Original post by manuel132)
how many times is 2.56 x 10^27 bigger than 5 x 10^5?

i do have the answers so but i don't know how to begin.. i had 50 weeks for the first one but according to the book i am wrong
Use:
20. (Original post by manuel132)
solve
at the start of the year, a traiin s half full. each week the number of people cathinng this increases by 1%
how many week will it be before the train is full?
Geometric series - does that help?

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