If x + y = 7 and xy = 4, then ﬁnd the value of x^2 + y^2.

2 answers:

6 0

X+y=7
xy=4

in xy=4, divide both sides by any variable (lets say i divide it y y)
xy=4
x=4/y
Now substitute it to the 1st equation
x+y=7
4/y+y=7
Multiply both sides by y
4+y^2=7y
Change to standard form
y^2-7y=4
Use the square of something...
y^2-7y+49/4=4+49/4
(y+7/2)^2=65/4
Squareroot both sides
y+7/2=posinega(sqrt of 65)/2
y=(sqrt of 65)/2-7/2
or y=-(sqrt of 65)/2-7/2

babunello [35]3 years ago

3 0

I don't know really how to do this stuff but I have learned in 7th grade and still working on it.

You might be interested in

How to solve (x+8) (x+6)

Alexandra [31]

Multiply each throughout!
=x^2+6x+8x+48
then arrange accordingly
x^2+14x+48
remember that in quadratic equation that you should have a squared (a) variable and a coefficient(b) and just a raw value (c)

5 0

3 years ago

Please please helpppp.

padilas [110]

There are 3 ways of solving a simultaneous problem, substitution method, elimination method and Gauss-Jordan method. I'm gonna use the substitution method since it's easier and i think it would suit your level more.

First let's try solving for y since it's easier to start with.

Firstly we have to find an equation for x:

$x-2y=2\\x-2y+2y=2+2y\\x=2+2y$