\(\text{Cho biểu thức:b=1990+720:(a-6) }\)
\(\text{Ta có: 1990+720:(a-6)=2000 Từ đó suy ra:}\)
\(\text{1990+720:(a-6)=2000}\)
\(\text{ 720:(a-6)=2000-1990}\)
\(\text{720:(a-6)=10 a-6 =720:10}\)
\(\text{a-6 =72 a =72+6 a =78}\)
B = 1990 + 720 : ( a – 6 )=2000
\(\Leftrightarrow\)720:(a-6)=10\(\Leftrightarrow\)a-6=72\(\Leftrightarrow\)a=78
2000=1990+720:(a-6)
2000-1990=720:(a-6)
10=720:(a-6)
720:10=a-6
72=a-6
72+6=a
78=a
đ/s:a=78
720:[a-6]=2000-1990=10
a-6=720:10=72
a=72+6=78
\(B=1990+720:\left(a-6\right)\)
\(\Leftrightarrow1990+720:\left(a-6\right)=2000\)
\(\Rightarrow720:\left(a-6\right)=2000-1990\)
\(\Rightarrow720:\left(a-6\right)=10\)
\(\Rightarrow a-6=72\)
\(\Rightarrow a=78\)