Toán Lớp 8: Tim X: a) (x + 5)2 + x(4 – x) – 18x = 53 b) (2x – 3)(x +7) – x(x + 6) – 5x + 16 = 0

Question

Toán Lớp 8:  Tim X: a) (x + 5)2 + x(4 – x) – 18x = 53  b) (2x – 3)(x +7) – x(x + 6) – 5x + 16 = 0

kimnguenoanh · Answer

a) (x+5)^2 +x(4-x)-18x=53   &hArr;x^2+10x+25+4x-x^2-18x=53   &hArr;-4x=53-25   &hArr;-4x=28   &hArr;x=-7   Vậy S={-7}   b) (2x-3)(x+7)-x(x+6)-5x+16=0   &hArr;2x^2+14x-3x-21-x^2-6x-5x+16=0   &hArr;x^2-5=0   &hArr;x^2=5   &hArr;x=+- sqrt{5}   Vậy S={+- sqrt{5}}

cattien · Answer

Giải đáp+Lời giải và giải thích chi tiết:      a) (x + 5)&sup2; + x(4 &ndash; x) &ndash; 18x = 53          &rArr; x&sup2;+10x+25+4x-x&sup2;-18x=53         &rArr; x&sup2;-x&sup2;+10x+4x-18x=53-25         &rArr; -4x=28         &rArr;x=-7     b) (2x &ndash; 3)(x +7) &ndash; x(x + 6) &ndash; 5x + 16 = 0         &rArr;2x&sup2;+14x-3x-21-x&sup2;-6x-5x+16=0         &rArr;2x&sup2;-x&sup2;+14x-3x-6x-5x=0+21-16         &rArr;x&sup2;=5         &rArr;x=5 h x=-5      Ch&uacute;c bn học tốt!       Xin ctlhn+5sao!