help Me please.
System of equations: Solve the system of equation
{xy=8}
{x2+y2=20}
xy = 8 Divide both sides of this equation by y .
x = 8/y Use this value for x in the second given equation.
x2 + y2 = 20
(8/y)2 + y2 = 20
64/y2 + y2 = 20 Multiply through by y2
64 + y4 = 20y2 Subtract 20y2 from both sides.
y4 - 20y2 + 64 = 0 We can rewrite this as...
(y2)2 - 20y2 + 64 = 0 Factor like this: u2 - 20u + 64 = (u - 4)(u - 16)
(y2 - 4)(y2 - 16) = 0 Factor each difference of squares.
(y + 2)(y - 2)(y + 4)(y - 4) = 0 Set each factor equal to zero.
y + 2 = 0 or y - 2 = 0 or y + 4 = 0 or y - 4 = 0
y = -2 or y = 2 or y = -4 or y = 4
Find x at each of these values for y .
When y = -2 , x = 8 / y = 8 / -2 = -4
When y = 2 , x = 8 / y = 8 / 2 = 4
When y = -4 , x = 8 / y = 8 / -4 = -2
When y = 4 , x = 8 / y = 8 / 4 = 2
The solution set is { (-2, -4), (2, 4), (-4, -2), (4, 2) }
xy = 8 Divide both sides of this equation by y .
x = 8/y Use this value for x in the second given equation.
x2 + y2 = 20
(8/y)2 + y2 = 20
64/y2 + y2 = 20 Multiply through by y2
64 + y4 = 20y2 Subtract 20y2 from both sides.
y4 - 20y2 + 64 = 0 We can rewrite this as...
(y2)2 - 20y2 + 64 = 0 Factor like this: u2 - 20u + 64 = (u - 4)(u - 16)
(y2 - 4)(y2 - 16) = 0 Factor each difference of squares.
(y + 2)(y - 2)(y + 4)(y - 4) = 0 Set each factor equal to zero.
y + 2 = 0 or y - 2 = 0 or y + 4 = 0 or y - 4 = 0
y = -2 or y = 2 or y = -4 or y = 4
Find x at each of these values for y .
When y = -2 , x = 8 / y = 8 / -2 = -4
When y = 2 , x = 8 / y = 8 / 2 = 4
When y = -4 , x = 8 / y = 8 / -4 = -2
When y = 4 , x = 8 / y = 8 / 4 = 2
The solution set is { (-2, -4), (2, 4), (-4, -2), (4, 2) }
System of equations: Solve the system of equation
{xy=8}
{x2+y2=20}
Formula:
\(\begin{array}{|rcll|} \hline (x+y)^2 &=& x^2+2xy+y^2 \\ x^2+y^2 &=& (x+y)^2-2xy \quad & | \quad xy = 8 \\ x^2+y^2 &=& (x+y)^2 - 8 \\ \hline \end{array}\)
1.
\(\begin{array}{|rcll|} \hline x^2+y^2 &=& 20 \quad & | \quad x^2+y^2 = (x+y)^2-16 \\ (x+y)^2-16 &=& 20 \\ (x+y)^2 &=& 20+16 \\ (x+y)^2 &=& 36 \\ \mathbf{x+y} &\mathbf{=}& \mathbf{\pm 6} \\ \hline \end{array}\)
Two Systems of equation now:
\(\begin{array}{|lrcl|lrcl|} \hline (1)& xy &=& 8 &(1) & xy &=& 8 \\ &\mathbf{y} &\mathbf{=}& \mathbf{\frac{8}{x}} & & \mathbf{y} &\mathbf{=}& \mathbf{\frac{8}{x}} \\\\ (2)& x+y &=& 6 &(2)& x+y &=& -6 \\ & x+\frac{8}{x} &=& 6 & & x+\frac{8}{x} &=& -6 \\ & x^2+8 &=& 6x & & x^2+8 &=& -6x \\ & x^2-6x+8 &=& 0 & & x^2+6x+8 &=& 0 \\ & x_{1,2}&=& \frac{6\pm \sqrt{36-4\cdot 8} }{2} & & x_{3,4}&=& \frac{-6\pm \sqrt{36-4\cdot 8} }{2} \\ & x_{1,2}&=& \frac{6\pm 4 }{2} & & x_{3,4}&=& \frac{-6\pm 4 }{2} \\ & x_{1,2}&=& 3\pm 1 & & x_{3,4}&=& -3\pm 1 \\\\ & \mathbf{x_1 =4} && \mathbf{x_2 = 2} & & \mathbf{x_3 = -2} && \mathbf{x_4 =-4} \\ & \mathbf{y_1} =\frac{8}{4}\mathbf{=2} && \mathbf{y_2} = \frac{8}{2}\mathbf{=4} & & \mathbf{y_3} = \frac{8}{-2}\mathbf{=-4} && \mathbf{y_4} = \frac{8}{-4}\mathbf{=-2} \\ \hline \end{array} \)