A. 2u+4<2 => u+2<1 => u<-1
B. 4u+1 < 21 => 4u < 20 => u<5
Here we need to combine the two inequalities, namely check for overlaps before writing in interval notation.
since u<-1 is already part of u<5, the solution set is u<-1, since u=0 (for example) will not satisfy the first inequality.
we write in interval notaion:
(-inf, -1)
the parentheses ( or ) mean the value closest to it is excluded.
the two values are the lower and upper bounds of the interval.
Here we mean the solutions are from -infinity (but excluded, because infinity is not a number) all the way up to -1, but -1 is also excluded because of the sign < (and not <=).
If the boundary value is to be included, we use the bracket.
For example, u<=-1 would be (-inf, -1].
