Adjusted little explicit and very brief and no escalation in the exercises

I am very disappointed in this book that I bought for my daughter's ECE prepa ... I accompany in mathematics and we are all the more possible exercises on all the topics of the program. We try several books. To speak of it, I find it very unfortunate 1 / that the exercises are all very hard suite (there is no basic training on each topic and no escalation of difficulty in exercises) 2 / More seriously, the corrected are succinct as to be incomprehensible and here it is unacceptable!