document.write( "Question 535981: One solution of kx^2-5x+k=0 is 3. Find the other solution \n" ); document.write( "
Algebra.Com's Answer #352095 by bucky(2189)\"\" \"About 
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Problem: if one solution of the quadratic equation:
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\n" ); document.write( "\"kx%5E2+-+5x+%2B+k+=+0\"
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\n" ); document.write( "is 3, what is the other solution?
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\n" ); document.write( "Notice that when you term-by-term compare the given equation to the standard form of the quadratic equation:
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\n" ); document.write( "\"ax%5E2+%2B+bx+%2B+c+=+0\"
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\n" ); document.write( "you can see that \"a\" correlates to k, \"b\" equals -5, and \"c\" also equals k.
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\n" ); document.write( "We know that the quadratic formula applies to solving a quadratic equation in the standard form. The quadratic formula says that for a quadratic equation in the standard form x can be found from:
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\n" ); document.write( "\"x+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+\"
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\n" ); document.write( "into this formula we can substitute k for \"a\" and \"c\" and -5 for \"b\" to get:
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\n" ); document.write( "\"x+=+%28-%28-5%29+%2B-+sqrt%28+%28-5%29%5E2-4%2Ak%2Ak+%29%29%2F%282%2Ak%29+\"
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\n" ); document.write( "The \"-%28-5%29\" becomes + 5 and the \"%28-5%29%5E2+=+25\" and \"k%2Ak+=+k%5E2\". These actions result in:
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\n" ); document.write( "\"x+=+%285+%2B-+sqrt%28+25-4%2Ak%5E2+%29%29%2F%282%2Ak%29+\"
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\n" ); document.write( "multiply both sides by 2*k which is the denominator on the right side. This clears the denominator, and the formula becomes:
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\n" ); document.write( "\"2%2Ak%2Ax+=+5+%2B-+sqrt%28+25-4%2Ak%5E2+%29+\"
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\n" ); document.write( "we also know that one value for x is 3. We were told that in the statement of the problem. So substitute 3 for x in the formula. This makes the left side become:
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\n" ); document.write( "\"2%2Ak%2A3+=+5+%2B-+sqrt%28+25-4%2Ak%5E2+%29+\"
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\n" ); document.write( "multiply out the left side to get:
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\n" ); document.write( "\"6%2Ak+=+5+%2B-+sqrt%28+25-4%2Ak%5E2+%29+\"
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\n" ); document.write( "get rid of the 5 on the right side by subtracting 5 from both sides:
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\n" ); document.write( "\"6%2Ak+-+5+=+0+%2B-+sqrt%28+25-4%2Ak%5E2+%29+\"
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\n" ); document.write( "square both sides to get rid of the radical on the right side and this formula becomes:
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\n" ); document.write( "\"36%2Ak%5E2+-+60k+%2B+25+=+25-4%2Ak%5E2++\"
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\n" ); document.write( "cancel 25 on both sides of the formula by subtracting 25 from both sides. Also get rid of the \"-4%2Ak%5E2\" on the right side by adding \"4%2Ak%5E2\" to both sides to get:
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\n" ); document.write( "\"40%2Ak%5E2+-+60k+=+0\"
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\n" ); document.write( "Factor a k from terms on the left side:
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\n" ); document.write( "\"k%2A%2840k+-+60%29+=+0\"
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\n" ); document.write( "notice that this equation will be true if either of the two factors on the left side is equal to zero because multiplication by a zero results in the left side becoming zero and making the left side equal to the zero on the right side.
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\n" ); document.write( "So this formula will be true if either k = 0 or if 40k - 60 = 0. We can ignore k = 0 because if this were true in the original quadratic equation of the problem if k were zero, both the
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\n" ); document.write( "then dividing both sides by 60:
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\n" ); document.write( "\"k+=+60%2F40\"
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\n" ); document.write( "and reducing the right side by dividing both the numerator and denominator by 20 to get:
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\n" ); document.write( "\"k+=+3%2F2\"
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\n" ); document.write( "Now we can go back to the original problem and substitute \"3%2F2\" for k to make it become:
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\n" ); document.write( "\"%283%2F2%29x%5E2+-+5x+%2B+3%2F2++=+0\"
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\n" ); document.write( "Multiply all terms by 2 to cancel out the denominator and you have:
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\n" ); document.write( "\"3x%5E2+-+10x+%2B+3+=+0\"
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\n" ); document.write( "compared to the standard quadratic equation we now have \"a\" = 3, \"b\" = -10, and \"c\" = 3. Substituting these values into the quadratic formula, we get:
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\n" ); document.write( "\"x+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+\"
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\n" ); document.write( "which becomes:
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\n" ); document.write( "\"x+=+%28-%28-10%29+%2B-+sqrt%28+%28-10%29%5E2-4%2A3%2A3+%29%29%2F%282%2A3%29+\"
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\n" ); document.write( "Simplifying to:
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\n" ); document.write( "\"x+=+%2810+%2B-+sqrt%28100-36%29%29%2F6\"
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\n" ); document.write( "The radical term becomes the square root of 64:
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\n" ); document.write( "\"x+=+%2810+%2B-+sqrt%2864%29%29%2F6\"
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\n" ); document.write( "which simplifies to:
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\n" ); document.write( " and this simplifies to \"x+=+3\"
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\n" ); document.write( "and
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\n" ); document.write( "\"x+=+2%2F6\" and this simplifies to \"x+=+1%2F3\"
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\n" ); document.write( "The first value for x we already knew because it was part of the problem. The second value for x, which we found was \"x+=+1%2F3\", is the answer you were asked to find in the problem.
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\n" ); document.write( "Hope this helps you to understand the quadratic equation a little better and how to apply that knowledge to solving this problem.
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\n" ); document.write( "Check my work. It's late and I might have introduced some errors due to lack of coffee. You can also check this problem by multiplying the two factors:
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\n" ); document.write( "\"%283%2F2%29%2A%28x+-+3%29%2A%28x+-+1%2F3%29\" and see if the answer does not give you the original equation in the problem in which \"k+=+3%2F2\"
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\n" ); document.write( "Good luck ...
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