He can check by substituting (1) for x.

3(3x+6) = 4(7x−1) 
3(3·1+6) = 4(7·1−1)
3(3+6) = 4(7-1)
3(9) = 4(6)
27 = 24

False so there is a mistake.


3(3x+6) = 4(7x−1) 
9x+18 = 28x−1        <--should be   9x+18 = 28x−4
9x−9x+18 = 28x−9x−1  <--should be   9x−9x+18 = 28x−9x−4
18 = 19x−1           <--should be   18 = 19x-4
18+1 = 19x−1+1       <--dhould be   18+4 = 19x-4+4 
19 = 19x             <--should be   22 = 19x 
1 = x                <--should be    = x

Common error in distributing: A(B + C), forgetting to 
multiply the A by the C.

Check the terribly ugly answer 



















Trouble is, when you get a terribly ugly solution such as ,
to check the terribly ugly answer is much harder than solving
the equation.

Edwin