some problems with solutions (1 Viewer)

[lyounamu]

Have anyone of you guys encountered any problem with the solution for cambridge?

I am having some issues with the solution at the moment...as the answer there doesn't seem entirely right.

For example, look at this:

mod (z1+z2) >= abs (mod (z1) + mod (z2)) = 25-6 = 19

I think this is wrong. It should have been mod(z1) - mod(z2) not +

and another one: this is Q6 from exercise 2.3 solution

I don't really understand the last line of its solution, can anyone care to explain? Thanks.

 

[clintmyster]

Im not too sure but ums all i can think of right now that may be somewhat useful is that whole triangle inequality thing that the |z1| + |z2| >= |z1 + z2|

 

[lyounamu]

Im not too sure but ums all i can think of right now that may be somewhat useful is that whole triangle thing that the |z1| + |z2| >= |z1 + z2|

Yeah I know that but this is little different one. You use that to find the largest value.

You use the diffrent one to find the smallest value of mod (z1+z2)

 

[clintmyster]

Yeah I know that but this is little different one. You use that to find the largest value.

You use the diffrent one to find the smallest value of mod (z1+z2)

In that case what you said about it being a minus is probably right.

 

[kaz1]

Have anyone of you guys encountered any problem with the solution for cambridge?

I am having some issues with the solution at the moment...as the answer there doesn't seem entirely right.

For example, look at this:

mod (z1+z2) >= abs (mod (z1) + mod (z2)) = 25-6 = 19

I think this is wrong. It should have been mod(z1) - mod(z2) not +

and another one: this is Q6 from exercise 2.3 solution

I don't really understand the last line of its solution, can anyone care to explain? Thanks.

I remember doing the first question. Is it Q7 from 2.3? If it is you find find the |z| of 24 + 7i and the locus of |z₁ + z₂| is a circle of radius 6 that goes around the point on the Argand diagram representing 24+7i. Since you found that the modulus of 24+7i is 25 the minimum modulus of |z₂ +z₁| would be the vector going down along the vector of z₁ by 6. Since your going down the modulus would decrease thus that is where you get 25-6=19

Hope that made sense.

 

[Trebla]

I think a similar question was asked before:
http://community.boredofstudies.org...se-complex-numbers-triangular-inequality.html

 

[lyounamu]

I remember doing the first question. Is it Q7 from 2.3? If it is you find find the |z| of 24 + 7i and the locus of |z₁ + z₂| is a circle of radius 6 that goes around the point on the Argand diagram representing 24+7i. Since you found that the modulus of 24+7i is 25 the minimum modulus of |z₂ +z₁| would be the vector going down along the vector of z₁ by 6. Since your going down the modulus would decrease thus that is where you get 25-6=19

Hope that made sense.

Yeah, that's a very good approach to solving this question. Thanks

 

[azureus88]

hey, what about q12 for Further Questions 4 on Polynomials? can someone explain how to do it. i dont get the last bit (http://img399.imageshack.us/img399/3015/mathsfn7.png)