Proszę was o pomoc w zadaniu z matematyki


1. [tex]\frac{10x-5}{5} = \frac{5(2x-1)}{5} = 2x-1[/tex] odp:c
2. 2(2x-3)-3(x-4)=4x-6-3x+12=x+6
3. (5m-2n)(3m+n)=15[tex]m^{2}[/tex]+5mn-6mn-2[tex]n^{2}[/tex]=15
4. (a+b)-(a+b)=a+b-a-b=0