solution:

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x² - xx + 4 = x
xxxxx xxxxxxx

xxxx 3x x x = x² x 2*(3/2)*x x xxxxxxx x (3/2)² + 4
x xxxxxxxxx - xxx + 16/4 x (x-3/2)² + xxx
xxxx the xxxxxxxx is xxxxxxxxxx to xxxxxxxxx x xxx x 0
xxx we xxxxxxxx xxxx xxxx is xxxxxxxxxx xxxxxxx xxxxxxxxx >x x xxx xxx x
xxxx (x-3/2)² x 7/4 >= xxx for xxx x ( xxxx xxxxxxxxx + xxx is xxxxx xxxx )
xxxx xxxx xxxxxxxx has no solution in x ( xxx xx xxxxxx

second method:

xxxxx = b² - xxx x (-3)² x xxxxx
= x - xx x xx
xxxxx xx xxxxxxxx thus xxx xxxxxxxx has no solutions in R