A)15-2x=-69 B)54+(x-87)=25-(87-54) C)9-3|x-2|=-6 D)(x^2-49)(7x+21)=0

a ) 15 - 2x = - 69 2x = ( - 15 ) - ( - 69 ) 2x = 54 x = 54 : 2 x = 27 b ) 54 + ( x - 87 ) = 25 - ( 87 - 54 ) 54 + ( x - 87 ) = - 8 x - 87 = ( - 8 ) - 54 x - 87 = - 62 x = ( - 62 ) + 82 x = 20 c ) 9 - 3| x - 2 | = 6 3| x - 2 | = 3 | x - 2 | = 3 ÷ 3 | x - 2 | = 1 TH1 : x - 2 = 1 TH2 : x - 2 = - 1 x = 1 + 2 x = - 1 + 2 x = 3 x = 1 Vậy x € { 1 ; 3 } d ) ( x^2 - 49 ) ( 7x + 21 ) = 0 TH1 : x^2 - 49 = 0 TH2 : 7x + 21 = 0 => x^2 = 49 7x = 0 - 21 => x = 7 7x = - 21 x = - 3