( 9x + 8 )( 80 - 9x ) = 1855方程两边乘以 -1 ,得( 9x - 80 )( 9x + 8 ) = -1855( 9x )" - 720x + 72x - 640 + 1855 = 081x" - 648x + 1215 = 0把系数化简81( x" ) - 81( 8x ) + 1200 + 15 = 081( x" ) - 81( 8x ) ...