Toán Lớp 8: a) x( x+6)- 7x- 42= 0 b) 25x^2- 9= 0 tìm x

Question

Toán Lớp 8:  a) x( x+6)- 7x- 42= 0 b) 25x^2- 9= 0 tìm x

doanthulan · Answer

a) x ( x + 6 ) - 7x - 42 = 0     &hArr; x ( x + 6 ) - 7 ( x + 6 ) = 0     &hArr; ( x + 6 ) ( x - 7 ) = 0     &hArr;  ( left[  begin{array}{l}x+6=0  x-7=0 end{array}  right. )      &hArr;  ( left[  begin{array}{l}x=-6  x=7 end{array}  right. )      Vậy x = - 6 ; x = 7     b) 25x^2 - 9 = 0     &hArr; 25x^2 - 3^2 = 0     &hArr; ( 5x - 3 ) . ( 5x + 3 ) = 0     &hArr;  ( left[  begin{array}{l}5x-3=0  5x+3=0 end{array}  right. )      &hArr;  ( left[  begin{array}{l}5x=3  5x=-3 end{array}  right. )      &hArr;  ( left[  begin{array}{l}x= frac{3}{5}  x=- frac{3}{5} end{array}  right. )      Vậy x = 3/5 ; x = - 3/5

phuongthaongoc · Answer

Giải đáp+Lời giải và giải thích chi tiết:   a)x(x+6)-7x-42=0   &rArr;x(x+6)-7(x+6)=0   &rArr;(x+6)(x-7)=0   TH1:x+6=0   &rArr;x=0-6   &rArr;x=-6   TH2:x-7=0   &rArr;x=0+7   &rArr;x=7   Vậy x&isin;{-6;7}   b)25x&sup2;-9=0   &rArr;(5x-3)(5x+3)=0   TH1:5x-3=0   &rArr;5x=0+3   &rArr;5x=3   &rArr;x=3:5   &rArr;x=3/5   TH2:5x+3=0   &rArr;5x=0-3   &rArr;5x=-3   &rArr;x=-3:5   &rArr;x=-3/5   Vậy x&isin;{-3/5;3/5}