Question

tìm x

a/ 2x(x-5)-x(3+2x)=26

b/ 49x²-81=0

Thanks may ban truoc nha !!

Answer 1

a/ 2x(x-5)-x(3+2x)=26

 =>2x²-10x-2x²-3x=26

=>-13x=26

=>x=-2

b/ 49x²-81=0

=>49x²=81

=>x²=\(\frac{49}{81}\)

\(\Rightarrow x^2=\left(-\frac{9}{7}\right)^2\)hoặc \(\left(\frac{9}{7}\right)^2\)

\(\Rightarrow x=\pm\frac{9}{7}\)

 

Answer 2

2x(x - 5) - x(3 + 2x) = 26

2x² - 10x - 3x - 2x² = 26

- 13x = 26

x = 26 : (- 13)

x = - 2

 

49x² - 81 = 0

(7x - 9)(7x + 9) = 0

Th1:

7x - 9 = 0

7x = 9

x = 9/7

Th2:

7x + 9 = 0

7x = - 9 

x = - 9/7

Vậy x = 9/7 hoặc x = - 9/7