19. D No matter what d is equal to, the answer on both sides will always be the same.
20. a. 2n-1=37 2n=38 n=19 whole number b. 2n+1=18 2n=17 n=17/2 not a whole number c. 3n+5=n+7 2n+5=7 2n=2 n=1 whole number d. n^2 +2=1 n^2=-1 n=i no solution Hope this helps.
