document.write( "Question 1181072: Which of the following equation has greatest and smallest number of real solutions?
\n" ); document.write( "(a) x^3 + x - 10 = 0
\n" ); document.write( "(b) x^2 + 4x - 15 = 0
\n" ); document.write( "(c) e^x - x = 0
\n" ); document.write( "(d) sec(x) - e^(-x^2)
\n" ); document.write( "Note: Here ^ means power.
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Algebra.Com's Answer #810906 by MathLover1(20850)\"\" \"About 
You can put this solution on YOUR website!
Which of the following equation has greatest and smallest number of real solutions?\r
\n" ); document.write( "\n" ); document.write( "(a) \"x%5E3+%2B+x+-+10+=+0\"...factor\r
\n" ); document.write( "\n" ); document.write( "\"x%5E3+%2B2x%5E2-2x%5E2%2B5x-4x+-+10+=+0\"\r
\n" ); document.write( "\n" ); document.write( "\"%28x%5E3+-2x%5E2%29%2B%282x%5E2-4x%29+%2B%285x-+10%29+=+0\"\r
\n" ); document.write( "\n" ); document.write( "\"x%5E2%28x+-2%29%2B2x%28x-2%29+%2B5%28x-+2%29+=+0\"\r
\n" ); document.write( "\n" ); document.write( "\"%28x+-+2%29+%28x%5E2+%2B+2x+%2B+5%29+=+0\"\r
\n" ); document.write( "\n" ); document.write( "one real solution is:\"x=2\"\r
\n" ); document.write( "\n" ); document.write( "find two more solutions for \"%28x%5E2+%2B+2x+%2B+5%29+=+0\"\r
\n" ); document.write( "\n" ); document.write( "use discriminant \"b%5E2-4ac\", if \"+b%5E2-4ac%3E0\" there will be real solutions\r
\n" ); document.write( "\n" ); document.write( "in your case \"a=1\", \"b=2\", \"c=5\"
\n" ); document.write( "\"+2%5E2-4%2A1%285%29%3E0\"
\n" ); document.write( "\"+4-20%3E0\"
\n" ); document.write( "\"+-16%3E0\"-> \"false\", so other two solutions are complex solutions\r
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\n" ); document.write( "\n" ); document.write( "(b) \"x%5E2+%2B+4x+-+15+=+0\"\r
\n" ); document.write( "\n" ); document.write( "use discriminant \"b%5E2-4ac\", if \"+b%5E2-4ac%3E0\" there will be real solutions\r
\n" ); document.write( "\n" ); document.write( "in your case \"a=1\", \"b=4\", \"c=-15\"\r
\n" ); document.write( "\n" ); document.write( "\"+4%5E2-4%2A1%28-15%29%3E0\"
\n" ); document.write( "\"+16%2B60%3E0\"
\n" ); document.write( "\"+76%3E0\"->true, so there are \"highlight%282%29\" real solutions\r
\n" ); document.write( "\n" ); document.write( "(c) \"e%5Ex+-+x+=+0\"
\n" ); document.write( "\"e%5Ex+=x+\"....take natural log of both sides
\n" ); document.write( "\"ln%28e%5Ex%29+=ln%28x+%29\"
\n" ); document.write( "\"x%2Aln%28e%29+=ln%28x+%29\"
\n" ); document.write( "\"x%2A1+=ln%28x+%29\"
\n" ); document.write( "\"x=ln%28x+%29\"->\"highlight%28No%29\" solution for \"x\" in \"R\"\r
\n" ); document.write( "\n" ); document.write( "(d) \"sec%28x%29+-+e%5E%28-x%5E2%29\"\r
\n" ); document.write( "\n" ); document.write( "set equal to zero
\n" ); document.write( "\"sec%28x%29+-+e%5E%28-x%5E2%29=0\"
\n" ); document.write( "\"sec%28x%29+=e%5E%28-x%5E2%29\"
\n" ); document.write( "only if \"x=0\"-> one real solution\r
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\n" ); document.write( "\n" ); document.write( "answer:
\n" ); document.write( "the equation b) \"x%5E2+%2B+4x+-+15+=+0\" has greatest number of real solutions
\n" ); document.write( "the equation c) \"e%5Ex+-+x+=+0\" has smallest number of real solutions\r
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