Dear all
AOA
I am bit confused about a particular problem of form and validity in categorical syllogism, please go through it and suggest where i am mistaken

consider these categorical syllogism of form AAA-3

all terriers are dogs
all terriers are mammals
therefore, all mammals are dogs

the second one is

all terriers are mammals
all terriers are dogs
therefore all dogs are mammals

both these are in standard form, having true premises and same form but former has false conclusion and so is invalid and later has true and so is a valid argument.

please justify it??

regards