Toán Lớp 7: Câu 1: a) 6x ²-x-5=0 b) 5x² -12x-17 =0 c) 7x² -6x-13=0

Question

Toán Lớp 7:  Câu 1:  a) 6x ²-x-5=0 b) 5x² -12x-17 =0 c) 7x² -6x-13=0

dinhcongson · Answer

Giải đáp+Lời giải và giải thích chi tiết: a)6x^2-x-5=0 <=>6x^2-6x+5x-5=0 <=>6x(x-1)+5(x-1)=0 <=>(x-1)(6x+5)=0 <=> ( left[ begin{array}{l}x-1=0 6x+5=0 end{array} right. ) <=> ( left[ begin{array}{l}x=1 x=- dfrac56 end{array} right. ) Vậy x=1 hoặc x=-5/6 b)5x^2-12x-17=0 <=>5x^2+5x-17x-17=0 <=>5x(x+1)-17(x+1)=0 <=>(x+1)(5x-17)=0 <=> ( left[ begin{array}{l}x+1=0 5x-17=0 end{array} right. ) <=> ( left[ begin{array}{l}x= dfrac{17}{5} x=-1 end{array} right. ) Vậy x=-1 hoặc x=17/5. c)7x^2-6x-13=0 <=>7x^2+7x-13x-13=0 <=>7x(x+1)-13(x+1)=0 <=>(x+1)(7x-13)=0 <=> ( left[ begin{array}{l}x+1=0 7x-13=0 end{array} right. ) <=> ( left[ begin{array}{l}x= dfrac{13}{7} x=-1 end{array} right. ) Vậy x=-1 hoặc x=13/7.

lyly98 · Answer

C&acirc;u 1:      a) 6x &sup2;-x-5=0         6x&sup2; - 6x +5x-5=0         6x(x-1)  + 5(x-1)=0          (x-1)(6x+5)       =0     &rArr; ( left[  begin{array}{l}x-1=0  6x+5=0 end{array}  right. )      &rArr;  ( left[  begin{array}{l}x=1  x=-5/6 end{array}  right. )     b) 5x&sup2; -12x-17 =0         5x&sup2; +5x - 17x -17=0        5x(x+1)  -17(x+1) = 0         (5x-17)(x+1) = 0     &rArr;  ( left[  begin{array}{l}5x-17=0  x+1=0 end{array}  right. )     &rArr;  ( left[  begin{array}{l}x=17/5  x=-1 end{array}  right. )     b) 7x&sup2; -6x-13=0      7x&sup2; + 7x -13x -13=0       7x(x+1) - 13(x+1)=0       (x+1)(7x-13) =0     &rArr; ( left[  begin{array}{l}x+1=0  7x-13=0 end{array}  right. )     &rArr; ( left[  begin{array}{l}x=-1  x=13/7 end{array}  right. )      Xin hay nhất      #datfsss