a) 1400 : 20 - (17 + x) = 20

70 - (17 + x) = 20

17 + x = 70 - 20

17 + x = 50

x = 50 - 17

x = 33

b) 8 \(\times\) (x + 15) = 640

x + 15 = 640 : 8 

x + 15 = 80

x = 80 - 15

x = 65

c) x \(\times\) 62 + x \(\times\) 38 = 4200

x  \(\times\) (62 + 38) = 4200

x \(\times\) 100 = 4200

x = 4200 : 100

x = 42

d) x \(\times\) 186 - x \(\times\) 86 = 3400

x \(\times\) (186 - 86) = 3400

x \(\times\) 100 = 3400

x = 3400 : 100

x = 34 

42 nha

X x 62 + X x 38 = 4200

X x (62+38)=4200

X=4200:100=42

Đáp số : 42

X x 62 + X x 38 = 4200

X x ( 62 + 38 ) =   4200

X x    100        =   4200

X                    = 4200: 100

X                    =   42

Đưa về:

x^2+100=4200

=> x^2=4200:100=42

x^2=42=> x=\(\sqrt{42}\)

ko biết đúng hay sai đây

=> x . ( 62 + 38 ) = 4200

=> x . 100 = 4200

=> x = 4200 : 100

=> x = 42

\(x\times62+x\times38=4200\)

\(x\times\left(62+38\right)=4200\) 

\(x\times100=4200\)

\(x=4200:100\)

\(x=42\)

\(x\times62+x\times38=4200\)

\(x\times\left(62+38\right)=4200\)

\(x\times100=4200\)

\(x=4200\div100=42\)

X x 62 + X x 38 = 4200

X x (62 + 38) = 4200

X x 100 = 4200

X = 4200 : 100

X = 42.

x(62 + 38) = 4200

100x = 4200

x = 4200 : 100

x = 42 

a)X x 62 + X x 38 = 4200                        b) X x 186 - X x 86 = 3400

   X x 62 + 38 =4200                                    X x 186 - 86 = 3400

   X x 100 = 4200                                         X x 100 = 3400

   X           = 4200 : 100                                X           = 3400 : 100

   X           = 42                                             X           = 34

                         c)X x 623 - X x 123 = 1000

                            X x 623 - 123 = 1000

                            X x 500 = 1000

                            X           = 1000 : 500

                            X           = 2