Question

determine o valor de ab-1, sabendo que a=0,777... e b=1,222...

Answer 1

ab - 1 = ?
a = 0,7777.......=7/9
b)1 ,2222........= 1 + 2/9 = 11/9
7/9 .  11/9 - 1 =
77/81 - 1 = 
m.m.c = 81
77/81-81/81 = -4/81

Answer 2

O.777...... = 7/9 *****
1,222. = INTEIRO   2/9 = 11/9
( 9 *1) + 2 = 11 CONSERVA DENOMINADOR

( a * b) - 1 =
( 2/9 * 11/9 ) - 1  =
22/81 - 1/1 = ( 22 - 81)/81 = -59/81