Toán Lớp 8: Tìm x : a) (x+8)(x+6)-x^2=104 b) 3x^2- (x+2) (3x-1)= -7

Question

Toán Lớp 8:  Tìm x : a) (x+8)(x+6)-x^2=104 b) 3x^2- (x+2) (3x-1)= -7

truongankimtrong · Answer

Giải đáp+Lời giải và giải thích chi tiết: a) (x+8)(x+6) - x² = 104 <=> x² + 14x + 48 - x² = 104 <=> 14x + 48 = 104 <=>14x = 104 - 48 <=> 14x = 56 <=> x = 56 : 14 <=> x = 4 Vậy x=4 b) 3x² - (x+2)(3x-1) = -7 <=> 3x² - 3x² - 5x + 2 = -7 <=> -5x + 2 = -7 <=> -5x = -7-2 <=> -5x = -9 <=> x = 9/5 Vậy x=9/5

cattien · Answer

Giải đáp:   $ a) (x+8)(x+6)-x&sup2;=104$     $&hArr;x(x+6)+8(x+6)&minus;x&sup2;=104$     $&hArr;x&sup2;+6x+8x+48&minus;x&sup2;=104$     $&hArr;14x+48=104$     $&hArr;14x=104-48$     $&hArr;14x=56$     $&hArr;x=4$     $b) 3x&sup2;-(x+2)(3x-1)=-7$     $&hArr;3x&sup2;&minus;[x(3x&minus;1)+2(3x&minus;1)]=&minus;7$     $&hArr;3x&sup2;&minus;[3x&sup2;&minus;x+2(3x&minus;1)]=&minus;7$     $&hArr;3x&sup2;&minus;(3x&sup2;&minus;x+6x&minus;2)=&minus;7$     $&hArr;3x&sup2;&minus;(3x&sup2;+5x&minus;2)=&minus;7$     $&hArr;3x&sup2;&minus;3x&sup2;&minus;5x+2=&minus;7$     $&hArr;&minus;5x+2=&minus;7$     $&hArr;-5x=-9$     $&hArr;x=9/5$              Ch&uacute;c bn hc tốt   ????             @LinhSad