document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1203435>Question 1203435</A>: <I><SPAN STYLE=\"word-break: break-all;\"> https://brainly.com/question/36509846 </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #838997 by </B><A HREF=/tutors/aboutme.mpl?userid=math_tutor2020><B>math_tutor2020(3821)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=math_tutor2020><IMG SRC=http://www.algebra.com/images/aboutme-small.gif BORDER=0 alt=\"About Me\" VALIGN=MIDDLE></A>&nbsp;<IMG SRC=http://www.algebra.com/images/nopicture.jpg><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=838997\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> <font color=black size=3><BR>\n" );
document.write( "The tutor @ikleyn has shown two great approaches.\r<BR>\n" );
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document.write( "I'll show two more methods.\r<BR>\n" );
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document.write( "Instead of y, I'll use x.\r<BR>\n" );
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document.write( "The task is to solve x^2 = 81 which is the same as x^2-81 = 0\r<BR>\n" );
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document.write( "Further we can write <BR>\n" );
document.write( "1x^2 + 0x + (-81) = 0\r<BR>\n" );
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document.write( "Compare that to the template<BR>\n" );
document.write( "ax^2 + bx + c = 0<BR>\n" );
document.write( "to find that:<BR>\n" );
document.write( "a = 1<BR>\n" );
document.write( "b = 0<BR>\n" );
document.write( "c = -81\r<BR>\n" );
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document.write( "Those values are plugged into the quadratic formula.<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=x+=+9 ALIGN=MIDDLE  ALT=\"x+=+9\"   DISABLED_style= \"max-width:90%; height:auto;\" > or  <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=x+=+-9 ALIGN=MIDDLE  ALT=\"x+=+-9\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "While this method takes a bit more work, I think it's still handy to know multiple approaches. \r<BR>\n" );
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document.write( "Another approach is to graph y = x^2 - 81 using a tool like Desmos or GeoGebra.<BR>\n" );
document.write( "This produces a parabola that opens upward. The parabola crosses the x axis at x = 9 and x = -9, which are the two solutions to x^2 = 81.\r<BR>\n" );
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document.write( "Window: xmin = -10, xmax = 10, ymin = -100, ymax = 100\r<BR>\n" );
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document.write( "Link to the interactive Desmos graph<BR>\n" );
document.write( "<a  rel=nofollow HREF=\"https://www.desmos.com/calculator/ewdbmqwf2c\">https://www.desmos.com/calculator/ewdbmqwf2c</a>\r<BR>\n" );
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document.write( "Therefore, the two solutions to y^2 = 81 are y = 9 or y = -9\r<BR>\n" );
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document.write( "As a quick check,<BR>\n" );
document.write( "y^2 = 81<BR>\n" );
document.write( "9^2 = 81<BR>\n" );
document.write( "9*9 = 81<BR>\n" );
document.write( "81 = 81<BR>\n" );
document.write( "and also<BR>\n" );
document.write( "y^2 = 81<BR>\n" );
document.write( "(-9)^2 = 81<BR>\n" );
document.write( "(-9)*(-9) = 81<BR>\n" );
document.write( "81 = 81<BR>\n" );
document.write( "When squaring the negative, the two negatives cancel out to get a positive.<BR>\n" );
document.write( "In other words: negative times negative = positive<BR>\n" );
document.write( "We get the same thing on both sides (81), so we have confirmed the answers are correct.<BR>\n" );
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