Mysterious Complex Numbers

Algebra Level 3

A gaussian integers is a complex number z = a + b i z = a + bi , where a a and b b are integers.

How many gaussian integers satisfy R e ( z ) + I m ( z ) < 21 |Re(z)|+|Im(z)| <21 ?


The answer is 841.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

1 solution

Ayush Kumar
Sep 1, 2017

This can be solved using some logic. Since, we have absolute values, we can see that there are two choices for each component of z, positive and negative. This leads us to four overall choices, (Re(z) is positive and Im(z) is positive, Re(z) is negative and Im(z) is positive, Re(z) is negative and Im(z) is negative, and Re(z) is positive and Im(z) is negative). This means that we ould look at just one, let's say the first, and then multiply all by 4. This is because the four parts are the same apart from signage. This means that the answer must be a multiple of 4. Our only choice that satisfies this is 840 \boxed{840} .

What would be your approach to solve the question if there would have been more than one options which are divisible by 4?

Ojasvi Sharma - 3 years, 9 months ago

Do you know why your solution is wrong?

Hint: When you want to "pair" things up, consider when they cannot be "paired". E.g. what number is neither positive nor negative?

Calvin Lin Staff - 3 years, 9 months ago

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...