Question

Encuentra el perímetro y el área de las circunferencias cuyas ecuaciónes son las siguientes:

a) x² + y² = √13

b) x² + y² = 4√5

Answer 1

x²+y²=13

2x+y=1  

I then tried to solve by substitution:  

y=1-2x

x²+(1-2x)²=13  

I then got a bit muddled up and wasn't sure how to expand (1-2x)²  

But the answer i got would not factorise into two brackets so i decided to use the quadratic formula:  

-b+/- sqrt ......

but this did not get the correct answer of:  

x=-1.2, y=3.4

x=2, y=-3  

Please help me because i don't have a clue what to do next!