# What is a long and complicated math equation that equals 15?

I need a long and complicated math problem that equals 15. I'm giving my cousin a gift card but I don't want to tell her what the amount is, i want her to figure it out.

### 7 Answers

- Anonymous1 decade agoBest Answer
x^2-10x+y^2-20y=-125 what is x+y=?

(Solution)

First complete the square

This is done by taking the x and y term (numbers in front of x and y not x^2 y^2) dividing it by 2 and squaring it and adding it to the other side so you get

x^2-10x+25+y^2-20y+100=0

now break it up

x^2-10x+25=0 and y^2-20y+100=0

trinomial factor it (draw an x put the last number on the top and the middle number on the bottom from each equation) now you want two numbers to put in the side of the x they will be the same number and must multiply to equal the top number and add to be the bottom number so for the x one i used used -5 (-5^2=25 and -5+-5=-10) and for the y i used -10 (-10^2=100 and -10+-10=-20) so those work now to write it in factored from its simply (x-5)^2+(y-10)^2=0 so now just take the opposite of the number in the ( ) for the answers so x=5 and y=10 because (5-5)^2+(10-10)^2=0 and to check you can plug it into the original equation to find that when x=5 and y=10 it will equal -125 as the original equations says so now x+y=5+10 which equals 15 the number you wanted :) hope that's long enough and i explained my process well enough

Source(s): Made it up :) - Anonymous1 decade ago
3 times 5 - 2 +6-4

- How do you think about the answers? You can sign in to vote the answer.
- 1 decade ago
Take the square root of 100 and multiply that by 5. Then add 30, minus 5, then divide by 5.

Not really long or complicated