+118702 CPhill's answer is a good one but it is more common to do it the other way around.
consider this
2(3a) this is 2 lots of 3a and the answer is 2*3a=6a
2(3a+4) is 2 lots of (3a+4) which is 2 lots of 3a plus 2 lots of 4 = 6a+8
(2+3)(3a+4) is 5 lots of (3a+4) but this can also be thought of as 2 lots of (3a+4) plus 3 lots of (3a+4)
so
(2a−b)(3a−2b)=2a(3a−2b)−b(3a−2b)=6a2−4ab−3ab−−2b2=6a2−4ab−3ab+2b2=6a2−7ab+2b2
See, our answers are the same. 
+130477 Re: (2a-b) (3a-2b) resultado
We can evaluate this in several ways. One way is to "disrtibute" (multiply) the first expression over both terms in the second. This gives us
[(2a-b)*(3a)] + [(2a-b)*(-2b)] which gives us
[6a2 - 3ab] + [ -4ab + 2b2] =
6a2 - 3ab - 4ab + 2b2 and combining "like" terms, we have
6a2 - 7ab + 2b2
We also could have distributed the second expression over the first.....the answer would have been the same!!!
+118702 CPhill's answer is a good one but it is more common to do it the other way around.
consider this
2(3a) this is 2 lots of 3a and the answer is 2*3a=6a
2(3a+4) is 2 lots of (3a+4) which is 2 lots of 3a plus 2 lots of 4 = 6a+8
(2+3)(3a+4) is 5 lots of (3a+4) but this can also be thought of as 2 lots of (3a+4) plus 3 lots of (3a+4)
so
(2a−b)(3a−2b)=2a(3a−2b)−b(3a−2b)=6a2−4ab−3ab−−2b2=6a2−4ab−3ab+2b2=6a2−7ab+2b2
See, our answers are the same.
