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Solve the system of equations algebraically x^2+y^2=100 x-y=2

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cununadelaur | Student, Undergraduate | eNoter

Posted February 23, 2011 at 12:39 AM via web

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Solve the system of equations algebraically

x^2+y^2=100

x-y=2

3 Answers | Add Yours

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giorgiana1976 | College Teacher | Valedictorian

Posted February 23, 2011 at 12:44 AM (Answer #1)

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We'll solve the system using substitution method.

We'll solve for x the 2nd equation:

x =  2 + y (3)

We'll substitute x into the 1st equation:

(2+y)^2+y^2=100

We'll expand the square:

4 + 4y + y^2 + y^2 = 100

We'll combine like terms:

2y^2 + 4y + 4 = 100

We'll divide by 2 and we'll move all terms to one side:

y^2 + 2y + 2 - 50 = 0

y^2 + 2y - 48 = 0

We'll apply quadratic formula:

y1 = [-2 + sqrt(4 + 192)]/2

y1 = (-2+14)/2

y1 = 6

y2 = -8

We'll substitute y1 and y2 into the 3rd equation:

x1 =  2 + y1

x1 = 2 + 6

x1 = 8

x2 = 2 + y2

x2 = 2 - 8

x2 = -6

The solutions of the system are: (8 ; 6) and (-6 ; -8).

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justaguide | College Teacher | (Level 2) Distinguished Educator

Posted February 23, 2011 at 12:50 AM (Answer #2)

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We have x^2 + y^2 = 100 and x - y = 2. We have to solve these equations for x and y.

x - y = 2

=> (x - y)^2 =2^2

=> x^2 + y^2 - 2xy = 4

substitute x^2 + y^2 = 100

=> 100 - 2xy = 4

=> 2xy = 96

=> xy = 48

substitute x = 2 + y

=> y(2 + y) = 48

=> y^2 + 2y - 48 = 0

=> y^2 + 8y - 6y - 48 = 0

=> y(y + 8) - 6(y + 8) = 0

=> (y - 6)(y + 8) = 0

=> y = 6 and y = -8

for y = 6, x = 8

for y = -8, x = -6

The required solution is (-6, -8) and (8, 6)

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atyourservice | TA , Grade 10 | Valedictorian

Posted June 26, 2014 at 1:55 AM (Answer #3)

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x^2+y^2=100

x-y=2

add y to both sides

x = 2 + y

plug in this number as x in the first problem:

(2+y)^2 + y^2 =100

4 + y^2 + y ^2 =100

combine like terms:

y^2 + y ^2 =100 -4

2y^2 = 96

divide by 2

y^2 = 48

find the squareroot:

y = 6.92820323 or 6.93

plug in the number as y to get x:

x-6.93=2

add 6.93 on both sides:

x = 8.93

x= 8.93 y= 6.93 or you can round it to x=9  y = 7

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