document.write( "Question 1202233: A parabola has equation y = 4x? + x + c. One x-intercept is -3. What is the value of c. \n" ); document.write( "

Algebra.Com's Answer #836904 by ikleyn(52787) $\"\"$ $\"About$

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\n" ); document.write( "A parabola has equation y = 4x^2 + x + c.
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document.write( "The condition says that if x= -3, then y = 0.\r\n" );
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document.write( "Let's write it as an equation\r\n" );
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document.write( "    0 = 4*(-3)^2 + (-3) + c\r\n" );
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document.write( "or, simplifying\r\n" );
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document.write( "    0 = 4*9 - 3 + c\r\n" );
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document.write( "    0 = 36 - 3 + c\r\n" );
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document.write( "    0 = 33 + c\r\n" );
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document.write( "    c = -33.\r\n" );
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document.write( "ANSWER.  c = -33.\r\n" );
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document.write( "CHECK.  So, we found out the the function is y = 4x^2 + x - 33.\r\n" );
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document.write( "        Let's substitute x= -3 in it.  You will get\r\n" );
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document.write( "        y = 4*(-3)^2 + (-3) - 33 = 4*9 - 3 - 33 = 36 - 3 - 33 = 0.   ! Correct !\r\n" );
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