document.write( "Question 481308: Solve: 2^2x - 3 * 2^x - 40 = 0 \n" ); document.write( "
Algebra.Com's Answer #330901 by lwsshak3(11628)\"\" \"About 
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Solve: 2^2x - 3 * 2^x - 40 = 0
\n" ); document.write( "**
\n" ); document.write( "let u=2^x
\n" ); document.write( "u^2=2^2x
\n" ); document.write( "..
\n" ); document.write( "u^2-3u-40=0
\n" ); document.write( "(u-8)(u+5)=0
\n" ); document.write( "u=8
\n" ); document.write( "or
\n" ); document.write( "u=-5
\n" ); document.write( "..
\n" ); document.write( "u=2^x=-5 (reject, 2^x > 0)
\n" ); document.write( "u=2^x=8=2^3
\n" ); document.write( "x=3 \n" ); document.write( "
\n" );