Solving Simultaneous Equations: x^2 + y^2 = 10 and y = 2x - 5

[Haroldingo]

Homework Statement

Sure I could do this by looking at the mark scheme, but i need to know HOW and WHY, so that in the future i can do these equations by myself. Thanks :)

by elimenating y, solve the simeltaneous equation

Homework Equations

x^2 + y^2 = 10
y = 2x - 5

The Attempt at a Solution

I thought i might have to make 5 the subject for the equation for this to work?

Outside of this my solution was to square it but that didn't work either..

 

[SammyS]

If y = 2x - 5 , what is y² ?

 

[Haroldingo]

If y = 2x - 5 , what is y² ?

(2x - 5) ² ?

 

[Mark44]

(2x - 5) ² ?

Now replace y² in the first equation with this expression, and solve the resulting quadratic.