Question

5x-7+2x=21

4x-3=2x+5

TÌm X

Answer 1

a) 5x - 7 + 2x = 21

5x + 2x - 7 = 21

7x - 7 = 21

7x = 21 + 7

7x = 28

x = 28:7

x = 4

b) 4x-3 = 2x+5

=> 4x - 2x = 5+3

2x = 8

x = 8:2

x = 4

Answer 2

\(a,5x-7+2x=21\)

\(\Rightarrow\left(5x+2x\right)-7=21\)

\(\Rightarrow7x-7=21\)

\(\Rightarrow7x=21+7\)

\(\Rightarrow7x=28\)

\(\Rightarrow x=28\div7\)

\(\Rightarrow x=4\)

\(b,4x-3=2x+5\)

\(\Rightarrow4x-2x=5+3\)

\(\Rightarrow2x=8\)

\(\Rightarrow x=8\div2\)

\(\Rightarrow x=4\)

Answer 3

\(5x-7+2x=21\)\(\Leftrightarrow7x=21+7\)\(\Leftrightarrow7x=28\)\(\Leftrightarrow x=4\)

\(4x-3=2x+5\)\(\Leftrightarrow4x-2x=5+3\)

                                    \(\Leftrightarrow2x=8\)\(\Leftrightarrow x=4\)