Х^2-у^2=12
(х-у)(х+у)=12
2*(х+у)=12
х=2+у
2*(2+у+у)=12
4+4у=12
4у=12-4
4у=8
у=2
х=2+2=4
отв. х=4, у=2
( 3x - 4 )( 5x - 3 ) - 15x^2 = 47
15x^2 - 9x - 20x + 12 - 15x^2 = 47
- 29x = 47 - 12
X = 35 : ( - 29 )
X = - 35/29
X = - 1 6/29
-11х -220 -10х= -2010-2011
-11х-10х=+2010-2011+220
-21х=-4021-220
-21х= -3801
х=-3801:(-21)
х=181