Question

Find a value of X so that the figure is a square.

Answer 1

Hello !
We know that a square has all equal sides.

That means the side 3x+39 is equal to the side 3(5x-3):
            

           3x+39 = 3(5x-3)
           3x+39 = 15x-9   | - 3x 
           3x-3x+39 = 15x-3x-9
                   39 = 12x-9  | + 9
                   39 + 9 = 12x-9+9
                   48 = 12x  | ÷ 12
                   x = 48/12 ⇔ x = 4

 


So,one side is 3*4 + 39 = 12 + 39 = 51
And the other side is 3(5*4 - 3) = 3(20-3) = 3*17 = 51



As you can see,the sides are equal.

Answer 2

3(5x-3)=3x+39
15x-9=3x+39
12x=48
x=4