a)
[tex]a=2\\\\50-2a=50-2\cdot2=50-4=\boxed{46}[/tex]
b)
[tex]a=-1\\\\10a^2=10\cdot(-1)^2=10\cdot1=\boxed{10}[/tex]
c)
[tex]a=-2\\\\a+3a^2=-2+3\cdot(-2)^2=-2+3\cdot4=-2+12=12-2=\boxed{10}[/tex]
d)
[tex]a=1, \ b=2\\\\6a+2b=6\cdot1+2\cdot2=6+4=\boxed{10}[/tex]
e)
[tex]a=0,5\\\\4a-2=4\cdot0,5-2=2-2=\boxed0[/tex]
