Bài 1: 

b: \(\dfrac{72-x}{7}=\dfrac{x-70}{9}\)

=>648-9x=7x-490

=>-16x=-1138

hay x=569/8

c: \(\Leftrightarrow x^2=\dfrac{36}{25}\)

hay \(x\in\left\{\dfrac{6}{5};-\dfrac{6}{5}\right\}\)

d: Đặt x/5=y/4=k

=>x=5k; y=4k

Ta có: xy=180

\(\Leftrightarrow20k^2=180\)

\(\Leftrightarrow k^2=9\)

Trường hợp 1: k=3

=>x=15; y=12

Trường hợp 2: k=-3

=>x=-15; y=-12

program CapSoChinhPhuong;

uses crt;

var

      n, a, b, count: integer;

begin

      clrscr;

      write('Nhap vao so nguyen n: ');

      readln(n);

      count := 0;

      writeln('Cac cap so a, b sao cho a^2 + b^2 la so chinh phuong la:');

      for a := 1 to n do begin

            for b := 1 to n do begin

                  if (sqr(a) + sqr(b)) mod round(sqrt(sqr(a) + sqr(b))) = 0 then begin

                        writeln('a = ', a, ', b = ', b);

                        count := count + 1;

                  end;

            end;

      end;

      writeln('Tong so cap so la: ', count);

      readln;

end.

DỄ

NHƯNG KO MUỐN LÀM

hổng cần

\(x = {-b \pm \sqrt{b^2-4ac} \over 2a}\)

\(a.\dfrac{1}{6}+\dfrac{1}{14}=\dfrac{14}{84}+\dfrac{6}{84}=\dfrac{20}{84}=\dfrac{5}{21}\\ b.\dfrac{1}{3}+\dfrac{4}{5}=\dfrac{5}{15}+\dfrac{12}{15}=\dfrac{17}{15}\)

\(\dfrac{1}{6}+\dfrac{1}{14}=\dfrac{14}{84}+\dfrac{6}{84}=\dfrac{5}{21}\)

\(\dfrac{1}{3}+\dfrac{4}{5}=\dfrac{5}{15}+\dfrac{12}{15}=\dfrac{17}{15}\)

a) abc = 346

b) abc = 543

c) ab = 15

d) abcd = 3251