document.write( "Question 30755: 2x squared minus 3x squared minus 10x plus 15 \n" ); document.write( "
Algebra.Com's Answer #17467 by sdmmadam@yahoo.com(530)\"\" \"About 
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\n" ); document.write( "2x squared minus 3x squared minus 10x plus 15 = 0
\n" ); document.write( "Then 2x^2-3x^2-10x+15 = 0
\n" ); document.write( " - x^2-10x+15 =0 ----(1)
\n" ); document.write( "(x^2+10x-15)=0 (dividing by (-1)
\n" ); document.write( "x^2+10x = 15
\n" ); document.write( "The LHS resembles a^2+2ab with a= x and b = 5.
\n" ); document.write( "We need b^2 to complete the square.
\n" ); document.write( "Therefore adding b^2 = 5^2 = 25 to both the sides
\n" ); document.write( "x^2+10x+25 = 15+25
\n" ); document.write( "(x+5)^2 = 40
\n" ); document.write( "Taking sqrt
\n" ); document.write( "(x+5) = +sqrt(40) or -sqrt(40) or
\n" ); document.write( "x = -5+sqrt(40) or x = -5-sqrt(40)
\n" ); document.write( "That is x = -5+ 2sqrt(10) or x = -5-2sqrt(10)
\n" ); document.write( "Answer: x = -5+ 2sqrt(10) or x = -5-2sqrt(10)
\n" ); document.write( "Verification:putting x = -5+ 2sqrt(10) in (1)
\n" ); document.write( "LHS = -[-5+ 2sqrt(10) ]^2-10[-5+ 2sqrt(10)]+15
\n" ); document.write( "=-[25+40-20sqrt(10)]+50-20sqrt(10)+15
\n" ); document.write( "= -65+20sqrt(10)+50-20sqrt(10)+15
\n" ); document.write( "=0
\n" ); document.write( "=RHs
\n" ); document.write( "Since surds occur in conjuagate pairs
\n" ); document.write( "there is no need to test the validity of the second value
\n" ); document.write( " \n" ); document.write( "
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