document.write( "Question 152180: y = x^2
\n" ); document.write( "x^2 + y^2 = 20\r
\n" ); document.write( "\n" ); document.write( "I know the answer is (ą2, 4) but I don't know why. Can someone please explain this to me? \n" ); document.write( "

Algebra.Com's Answer #111838 by oscargut(2103) $\"\"$ $\"About$

You can put this solution on YOUR website!
y = x^2
\n" ); document.write( "x^2 + y^2 = 20\r
\n" ); document.write( "\n" ); document.write( "let use 1st eq in 2nd eq\r
\n" ); document.write( "\n" ); document.write( "so y+(y^2)=20\r
\n" ); document.write( "\n" ); document.write( "y^2+y-20=0\r
\n" ); document.write( "\n" ); document.write( " $\"y+=+%28-1+%2B-+sqrt%28+1%5E2-4%2A1%2A-20+%29%29%2F%282%2A1%29+\"$
\n" ); document.write( " $\"y+=+%28-1+%2B-+9%29%2F2+\"$
\n" ); document.write( "then y=4 or y=-5\r
\n" ); document.write( "\n" ); document.write( "if y=-5 then x is not real
\n" ); document.write( "if y=4 then x^2=4 then x=2 or -2
\n" ); document.write( "solution is (2,4) and (-2,4)\r
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