DimitrisThymaras

$y=-5x^2-6x+10 <=> y'=-10x-6, y'=0 <=> x=-0.6$

$y= -5(-0.6)^2-6(-0.6)+10=11.8$

so $(x,y)=(-0.6,11.8)$

$x^2+18x+5 = 1(x+9)^2+(-76)$

$x^2+15x+k$ with a=1,b=15 and c=k we want double root so $\sqrt{b^2-4ac}=0 <=> \sqrt{15^2-4k}=0 <=> \sqrt{15^2} =\sqrt{4k}=0 <=> k=225/4$

$\frac{ \sqrt{1500}}{4π}=\frac{38.7298334621}{π}=\frac{38.7298334621}{3,14...}$~3.08202222031

Hi my friend

I found it thank you.

by which theorem? 

I don't know why don't show the letters...

1)3x+3y=10 

2)(-9x - 9y)/-3 = -30/-3 <=> 3x + 3y = 10        so 1) = 2) so have solution for every x,y 

Yes you are right There is no x and y!!!

x = - 1 - y  and replace this in the other 3(- 1 - y)=4 - 3y  <=> - 3 - 3y = 4 - 3y  so -3 = 4 is false and we dont have solutions

13+3x=13+2x <=> 13-13=2x-3x <=> 0=-x <=> x=0/-1 <=> x=0